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Abstinence, in relation to reproduction, is a voluntary act or practice of refraining from sex. Often times, people are abstinent in order to prevent pregnancy, as abstinence is the only form of birth control that is 100% effective. However, abstinence may be practiced for personal, religious, or other medical reasons. 

As a spermatozoon approaches the zona pellucida (outer glycoprotein membrane) of the oocyte, the membrane of the acrosome will fuse with the plasma membrane of the oocyte, allowing the contents of the acrosome (including enzymes and antigens) to break through the egg’s tough coating. This reaction is necessary for fertilization of the egg to occur.

Activin is a powerful protein that regulates and participates in many cellular functions, including the menstrual cycle, and more specifically, the production and release of a reproductive hormone called follicle stimulating hormone (FSH). Activin is made by most organs and controls cellular proliferation and differentiation. Loss of activin can result in profound early developmental defects. Activin is regulated by a closely related protein called inhibin. Both activin and inhibin control male and female reproduction, and an imbalance in either of these hormones can result in infertility in both men and women.

The adrenal cortex is the outer tissue later of the adrenal gland and is the production site of corticosteroid and androgen hormones. It is sub-divided into three layers (zones), each structurally unique and producing a separate class of hormones. The zona glomerulosa is the most superficial layer and produces mineralcorticoids, such as aldosterone, which is involved in the regulation of blood pressure. The zona fasciculata is the middle layer and produces glucocorticoids such as cortisol, which is involved in regulating metabolism. The innermost layer is the zona reticularis and produces androgens, including androstenedione, which is the precursor to testosterone. Because the gonadal tissues normally produce more androgens than the adrenal cortex, the latter is often considered a secondary site of androgen synthesis.

The adrenal medulla is the central, reddish-brown portion of the adrenal gland and is surrounded by the adrenal cortex. It consists of irregularly shaped cells grouped around blood vessels, which are intimately connected by the sympathetic division of the autonomic nervous system. The cells of the adrenal medulla produce, store, and release epinephrine (adrenaline), norepinephrine (noradrenaline), and a small amount of dopamine. These are the hormones involved in the fight-or-flight response, where the production of epinephrine increases heart rate and blood pressure, blood vessel constriction in the skin and gastrointestinal tract, smooth muscle dilation, and metabolism; norepinephrine has the opposite effect.

Refers to expectant mothers who are 35 years of age or older. While mothers of advanced maternal age can have healthy pregnancies, women over 35 are more likely to experience difficulty achieving pregnancy, and various pregnancies complications.

In endocrinology, an agonist is a chemical or hormone that is capable of stimulating a cell in a manner akin to another hormone. It usually acts as a hormone mimic and binds to the same receptor used by the mimicked hormone in order to induce a biological response.

Alginate is a polysaccharide found in the cell walls of algae. When mixed with calcium, alginate will form a solid-like gel used to encapsulate cells.

An allosome differs from a typical autosome in that it determines the sex of an individual (e.g. the X and Y chromosomes are allosomes). In humans, an ovum contains the X allosome, and a sperm contains either the X or Y allosome.

Amniocentesis is a prenatal test that allows one’s healthcare practitioner to diagnose health concerns, genetic diseases, and chromosomal abnormalities in the womb by extracting a sample of amniotic fluid. This is the fluid that surrounds the baby in the uterus during development, where fetal cells that contain important health information are present. Amniocentesis is typically performed when an expectant mother is between 15 and 18 weeks pregnant and, due to the small level of risk, is often times only advised for women who have an increased risk of giving birth to a baby with genetic defects. Amniocentesis cannot detect structural birth defects. It is also the most accurate way to determine the sex of the baby before birth.

The amniotic cavity is the fluid-filled space within the amniotic sac where the developing fetus resides.

The amniotic sac is a thin but tough pair of membranes (namely, the chorion and amnion) filled with fluid. The amniotic sac surrounds the growing embryo, and later, the fetus. It is tough, yet pliable and transparent and is crucial for a successful pregnancy outcome, as it provides necessary support and cushioning.

The fallopian tube is comprised of three parts. The ampulla is the secondary, dilated section of the tube and is the main site where fertilization commonly occurs in both mice and humans.

Anaphase is the stage of cell division (mitosis or meiosis) during which chromosomes separate and are pulled toward opposite poles of the cell by the spindle in preparation for cell division. In meiosis I, homologous pairs of chromosomes separate, resulting in two haploid sets of chromosomes, a reduction from the diploid set of chromosomes present at the start. In mitosis and meiosis II, sister chromatids separate.

The medical specialty that addresses male reproductive and sexual health. 

the inability to ejaculate semen upon climax. Men with this condition may be able to produce semen, but it does not exit the body during orgasm. 

Aneuploidy traces back to the point of cell division when chromosomes are not separated properly and refers to a state in which a cell or cells has/have too many or too few chromosomes. This is often seen in the form of trisomy, such as Trisomy 21 (Down syndrome), or monosomy, such as Turners Syndrome. In female gametes, aneuploidy can lead to miscarriages, infertility, and birth defects.

Anovulation is the absence of ovulation, or oocyte release from the ovary, in the menstrual cycle. Anovulation may be physiological before puberty, during pregnancy and lactation, or after menopause. It may also be pathological due to disorders affecting the ovaries, pituitary gland, or hypothalamus. Chronic anovulation accounts for about 30% of all cases of female infertility. The most common cause of chronic anovulation is polycystic ovarian syndrome (PCOS).

The anterior pituitary gland is the front portion of the pituitary gland. It secretes hormones that regulate many physiological processes, including growth, reproduction, lactation, and stress.

Anti-mullerian hormone (AMH) is a hormone secreted by the Sertoli cells in the embryonic developing testes of males. AMH represses the development of the Mullerian Duct (also called paramesonephric ducts, developing female reproductive tract). AMH is also secreted by granulos cells of preantral and smaller antral follicels in the adult ovary. During male embryonic development, AMH insures the regression of female structures (fallopina tubes, uterus, cervix, and upper vagina), enabling the proper development of the wolffian duct (male reproductive tract, vas deferens, seminal vesicles). In the female, AMH secretion occurs during the reproductive lifespan until menopause; because of this, AMH can be used as a marker of the ovarian reserve. 

The anus is the ring-shaped opening at the end of the gastrointestinal tract opposite from the mouth. It is also the end of the alimentary canal and the posterior most opening on the perineum. It controls the removal of feces (solid waste material) from the body.

Aromatase (also referred to as estrogen synthetase or estrogen synthase) is the key enzyme responsible for estrogen production. Aromatase enzymes act by accelerating the conversion of testosterone, an androgen, into estrogens. Estrogens have been shown to promote the growth of some breast cancers. Aromatase inhibitors can decrease estrogen levels and have been used for treating breast cancer, as well as other disorders.

Artificial insemination (AI) consists of introducing sperm directly into the female genital tract, without sexual intercourse. This technique is used for fertility purposes in humans (with the use of assisted reproductive technology or a sperm donation program) and in animals (to employ genetic selection for productivity or by using a sperm bank of endangered species). Fresh or frozen washed sperm is placed in the vagina using a conception device or in the uterus by means of a catheter at the time of ovulation to improve the chances of fertilization of the released oocyte(s).

The complete lack of semen in ejaculate. Men who experience this disorder may have the ability to orgasm, however, semen is not released at this time. 

Assisted reproductive technology (ART) refers to a set of clinical procedures developed to help women conceive (become pregnant). Examples of ART include in vitro fertilization, intracytoplasmic sperm injection, preimplantation genetic diagnosis, cryopreservation, and intrauterine insemination. Currently, it is estimated that four million children worldwide have been conceived using ART procedures.

Asthenospermia is the medical term for a condition in which a male’s sperm have reduced motility (the ability to swim or move). Genetic, idiopathic, and iatrogenic factors can result in this condition. Although male infertility is most commonly attributed to a low sperm count, having sperm with poor motility can lead to infertility, as well, because, once ejaculated, the sperm must be able to travel through the vagina, cervix, and uterus before reaching the fallopian tubes where fertilization will take place. To overcome infertility due to asthenospermia, assisted reproductive technology procedures can be utilized, such as intracytoplasmic sperm injection.

Reduced sperm motility. In complete asthenozoospermia, 100% of sperm in a sample are immobile. 

Autophagy is a form of programmed cell death in which lysosomes degrade unnecessary and dysfunctional cells. Autophagy can be a way to maintain energy levels in cells during periods of starvation. Autophagy and apoptosis can be differentiated by several morphological and biochemical markers.

A common condition which occurs 3-5 days after childbirth that is characterized by mood swings, feelings of anxiety, difficulty sleeping and trouble eating. If these symptoms worsen, or persist beyond 5 days, patients may be experiencing postpartum depression. 

The maternal side of the placenta.

Bioengineering (also referred to as biological engineering) is a field of science in which the principles of engineering are applied to biology and medicine. Often times, bioengineering is applied to human health in order to develop new technologies that model, modify, or control biological systems.

Bioethics is the study of ethical issues that arise due to advancements in biology, medicine, health care, health policy, and health science.

A biomaterial is any natural or synthetic material that is used for biological application. For example, the components of an artificial joint are biomaterials.

Bisphenol A (BPA) is an industrial chemical and endocrine disruptor that has been used to make certain plastics and resins since the 1960s. BPA remains controversial because of its potential to seep into foods or beverages kept in containers that are made with the compound. It also has the ability to seep into the body when handling products that contain the chemical. Studies with rodents have shown that exposure to BPA can interfere with reproductive function.

Black cohosh is an herbal supplement that is used to treat the symptoms of menopause, such as hot flashes, mood disturbances, and vaginal dryness. It is also sometimes used to treat the symptoms of menstruation, premenstrual syndrome, and to induce labor in pregnant women. Research is inconclusive as to its effectiveness.

A blastomere is a single cell of a pre-implantation stage embryo formed by cell division of the zygote following fertilization. Using the specific assisted reproductive technology known as preimplantation genetic diagnosis, a single blastomere is removed from an embryo, and genetic testing is performed on this cell, so that embryos free of genetic abnormalities are transferred back into the recipient.

Bone mineral density refers to the amount of calcium and other minerals that exist in a segment of bone. A bone mineral density test is used to assess bone strength, predict the risk of fracture, and can be used to diagnose osteoporosis (a common ailment in post-menopausal women).

Braxton Hicks contractions, also known as practice contractions or false labor pains, are irregular uterine contractions that may begin as early as the second trimester of pregnancy but are more commonly felt during the third trimester. These contractions are usually experienced as an uncomfortable cramping sensation in the lower abdomen. They do not lead to the onset of labor and usually disappear with rest. Braxton Hicks contractions are acknowledged as the body’s way of preparing for the birthing process. The term “Braxton Hicks” dates back to the first description of these contractions by an English doctor named John Braxton Hicks in 1872.

A breech birth is the birth of a baby from a breech presentation, which refers to the baby exiting the pelvis feet or buttocks first. It accounts for about 3-4 % of all singleton deliveries. Factors associated with breech birth include high parity with uterine relaxation, twin or multiple fetuses, preterm labor, changes in amniotic fluid volume (poly- or oligo-hydramnios), previous breech birth, placental anomalies (placenta previa or fundal placental implantation), fetal head anomalies (hydrocephaly or anencephaly), uterine anomalies, and pelvic tumors. Generally, a baby in the breech position will be delivered by Caesarean section, as vaginal delivery is associated with high risks to the life of the mother and child.

The fold of peritoneum that connect certain components of the female reproductive tract to the walls and floor of the pelvis. The broad ligament can be divided into three parts: the mesovarium which supports the ovaries, the mesometrium which supports the uterus, and the mesosalpinx which supports the fallopian tubes. 

Cancer is any type of malignant growth or tumor caused by abnormal and uncontrolled cell division.

Caspases are a class of cysteine proteases, or a type of enzyme, that break up or cleave other proteins. Caspases are involved in the initiation and execution of apoptosis (programmed cell death). The caspases transmit intracellular signals through a "caspase cascade" where one caspase cleaves a second caspase, and this cleavage activates the second caspase. Once activated, the second caspase could then cleave other caspases (thereby activating them) or other downstream ligands.

A state of refraining from sex, marriage or both. Celibacy is different from abstinence, in that individuals who practice celibacy often remain abstinent over a long period of time, whereas abstinence itself can sometimes be a short-term practice. 

Chemotherapy is the use of drugs, either administered orally or intravenously, to kill cancer cells. Many drugs used in standard chemotherapy regimens are cytotoxic and act to kill cells that divide rapidly. Unfortunately, for this reason, rapidly dividing healthy cells will be killed along with the unwanted cancer cells.

The fetal side of the placenta, in which the chorionic vessels arise. 

Chromatin is the complex of DNA, RNA, and proteins that compact chromosomes into a smaller volume, so that they fit inside the nucleus of a cell. The array of proteins in chromatin can also change the activity of genes.

Cilia are small, hair-like projections that line the fallopian tubes. They wave back and forth to help guide the egg from the ovaries to the uterus. If the cilia have been previously damaged by infection, they may not move the egg to the uterus as efficiently. This can lead to the development of an ectopic pregnancy.

Circumcision refers to the surgical procedure where the foreskin (prepuce) covering the head of the penis is removed. This procedure is usually performed on infants or young children in religious ceremonies. In parts of Africa and in other high-risk populations, the procedure is recommended to prevent the contraction of the HIV/AIDS virus.

The clitoral hood is a flap of skin that covers and protects the female clitoris, functioning like the foreskin in males.

A clutch refers to all of the eggs that are produced at a single time. In rodents, a clutch of eggs surrounded by cumulus cells can be found in the oviduct following ovulation.

Cohesin is a protein complex that holds sister chromatids together, thereby regulating their separation in anaphase of both mitosis and meiosis.

The moment that a sperm fertilizes an egg (in humans) to produce a zygote, which eventually develops into an embryo.

A technique to delete a specific gene in a specific tissue to understand the role of the individual gene. In contrast to traditional gene knockout that deletes genes in the whole body, this is induced by a Cre-LoxP recombination system that can eliminate tissue-specific genes at specific times.

A contraceptive is a drug, chemical, or physical barrier/device that aids in pregnancy prevention.

The corpus luteum (Latin for "yellow body") is a hormone-secreting gland that forms after a mature egg is released from an ovarian follicle. It is composed of granulosa- and theca-lutein cells and primarily secretes the steroid hormone, progesterone. If the egg is not fertilized, the corpus luteum will degenerate and form the corpus albicans.

Corticotropes are specialized cells of the anterior pituitary gland that produce and secrete the hormone corticotropin (ACTH).

Cross-linking is the process of linking two molecules with the use of chemical reactions; cross-links may be covalent bonds, electrostatic bonds, or hydrogen bonds.

Cryopreservation refers to the process of storing cells, tissues, or organs at very low temperatures, so they can remain viable and functional again when thawed. Cryopreservation is often used to preserve embryos created by in vitro fertilization, so they can be implanted into a woman’s uterus at a later date.

Cumulus cells are one of two functionally divided classes of granulosa cells in the antral follicle. They surround the oocyte to form the cumulus-oocyte complex and are released with the egg during ovulation. In order for fertilization to occur, the sperm must penetrate through the layer of cumulus cells. An abundance of cumulus cells is necessary for the development of a healthy embryo, as they provide the necessary nutrients and energy for oocyte maturation.

Ovarian cysts are fluid-filled sacs formed in the ovaries. There are a few different types, but the most common are follicular or luteal cysts, which are formed during ovulation when the egg is not properly released from the follicle and remains in the ovary, or when the corpus luteum does not break down and dissolve after release of the oocyte. These cysts often disappear in a matter of months, but more serious cysts may cause abdominal pain and bleeding.

Cytokinesis is the division of the cytoplasm in a single cell for the purpose of forming two new daughter cells during mitosis and meiosis.

The highly vascularized, modified mucosal lining of the endometrium that is established through the process of decidualization. If an embryo does not implant in the decidualized uterus, the lining of the uterus is shed during the next period of menstruation. However, if implantation occurs, the decidua is maintained, and becomes the main source of nutrients for the developing fetus throughout the early weeks of pregnancy, until placenta becomes capable of assuming this responsibility.

A surgical procedure used to remove tissue from the inside of the uterus, often to clear out damaged or infected tissue, to assess the endometrium, or to terminate a pregnancy

Diploid is the designation given to cells with two sets of chromosomes; this is characteristic of somatic cells. In humans, this is 46 chromosomes (or 23 pairs).

Ductal is a term used to describe channels leading from glands or organs in the body. Ductal is commonly referenced in discussion of lactiferous ducts, which are responsible for carrying milk from the mammary gland to the nipple of a breast.

The ectoderm is the outermost layer of cells of a eukaryote or the outermost layer of cells in the developing embryo once it has reached the gastrula stage. This cell layer ultimately gives rise to nervous tissue, skin, mammary glands, pituitary gland, and enamel of the teeth.

An effector is a protein, often an enzyme, within a hormonally stimulated cell that helps produce the end result of the hormonal stimulation. Known effectors include transcription factors involved with altering cellular gene transcription, enzymes controlling the storage and retrieval of intracellular glucose, enzymes that produce steroid hormones, and intracellular structural proteins that control cellular shape and movement. These molecules often use intracellular energy stores and result in the amplification of hormonal signals, so that binding of a few hormone molecules can make cells do things that would otherwise be impossible, if they only depended on the energy from binding the hormone molecules, themselves.

Egg activation refers to a series of events that occur in the egg after it is fertilized by a sperm. These events include completion of meiosis, initiating the block to polyspermy, and translation of specific mRNAs from the egg that are necessary for embryonic development prior to the maternal to zygotic transition. In all animal species studied to date, a rise in calcium levels within the egg triggers all events of egg activation.

Egg donation is the process in which a woman (egg donor) volunteers to donate an egg/oocyte or several oocytes to another woman in the hopes of helping her become pregnant through the process of in vitro fertilization (IVF). Egg donation can be part of the process of third–party reproduction. Known egg donation is reserved for those individuals or couples who select a family member or friend to be their egg donor. Anonymous egg donation is when the donor is unknown to the patient or intended couple. Many times, egg donation is anonymous. An egg donor is typically given a thorough medical exam before being treated with hormones to induce hyperovulation. Following hormonal treatment, approximately 10-15 eggs are harvested to be screened for future IVF.

Ejaculation is the release of semen from the urethral opening of the penis and is usually accompanied by orgasm.

An embryo is an organism in its early stages of development. In humans, this stage extends from the time an egg undergoes fertilization to eight weeks after fertilization. Beyond that point, the organism is then referred to as a fetus.

Embryo donation utilizes unused embryos or embryos specifically created via donor eggs and donor sperm. The donated embryo is placed into the uterus of the future mother or the surrogate mother.

The embryonic disk is the flat, disk-shaped conceptus that forms prior to gastrulation in some vertebrates.

Emergency contraception is a form of birth control that may be used for up to five days after sexual intercourse has taken place. Emergency contraception is often used when no contraceptive methods were used, when the one or more birth control methods used may have failed, or when a woman was made to have sex against her will. The options for emergency contraception are emergency contraceptive pills and the Copper-T Intrauterine Device. These methods are not as effective as primary birth control methods used before or during sex.

Endocrinology is the study of the body’s endocrine glands and their secretions (known as hormones).

Endometriosis is a condition in which cells of the uterine lining, or endometrium, grow outside of the intrauterine environment, often on or around surrounding structures. This results in potential pain, bleeding, and scarring of internal reproductive structures, and, in some cases, infertility.

The epiblast is a tissue type of the upper side of the embryonic disk, which arises from the inner cell mass during the late blastula and early trophoblast stages of embryonic growth. These cells give rise to the tissues of the embryo proper.

Episiotomy is a small surgical incision along the midline of the perineum, the tissue between the vagina and anus, to enlarge the vaginal opening and facilitate vaginal delivery. It can be performed under local or epidural anesthesia, and it is sutured immediately after the delivery.

Estrogen is a steroid hormone that is produced primarily in the female ovaries and, in small amounts, in the adrenal cortex, male testes, and placenta. Estrogen helps regulate and guide female sexual development and reproductive system functions, such as the estrous and menstruation cycles.

The estrous cycle, which has been studied extensively in rodents, refers to the cyclic alterations that occur in the female reproductive tract and in sexual receptivity. The estrous cycle is often likened to the menstrual cycle in humans. It is composed of four distinct stages – proestrus, estrus, metestrus, and diestrus – that are each characterized by distinct physiology as well as animal morphology and behavior. Proestrus is the portion of the cycle when eggs reach full maturity within the follicles. External examination of the female genitalia reveals a swollen vulva and open vagina. Estrus is the stage of the cycle when ovulation occurs. The vagina remains open, and, at this stage, females are maximally receptive to males. Metestrus is the stage when the mature egg moves through the fallopian tube, and the vagina is closed. If successful copulation and fertilization occur, pregnancy will occur. If pregnancy does not occur, diestrus will ensue. Diestrus is the final stage of the estrous cycle in which unfertilized eggs are eliminated, and the vagina remains closed. During this stage, a new cohort of follicles begins rapid growth to prepare for ovulation in the next cycle.

ex situ refers to any procedure where the cells of interest are examined outside of their native environment.

An extra-amniotic pregnancy occurs when the amniotic sac ruptures, and the baby develops in the extra-embryonic coelom.

A person who belongs to the sex that produces eggs, and that is capable of childbearing. Human females typically have two X chromosomes. 

Fertility preservation is the use of specific medical interventions to protect the fertility of individuals whose disease or disease treatment may lead to infertility.

Fertilization is the event that occurs when a sperm and an egg unite to produce a zygote. During normal fertilization, the haploid male and female gametes fuse to produce a diploid zygote.

A fetal membrane is the tissue surrounding the fetus that works to protect, nourish, and assist in the excretion and respiration of the developing fetus. The fetal membranes include the chorion, amnion, and allantois. Healthy fetal membranes are required for favorable pregnancy outcomes.

In humans, the term fetus is used to describe a developing organism that has reached the eighth week of developmental age (following fertilization).

Fimbria is a fringe or fingerlike structure located at the ends of fallopian tubes. Fimbriae facilitate egg movement through the fallopian tubes.

Fixation is the process of preserving tissue through chemical means to retain its structure.

The follicle is the basic functional unit of the ovary.

A follicle that has progressed from the primary to the secondary, more mature stage of growth will display an accumulation of follicular fluid known as the follicular antrum.

The follicular phase is the portion of the menstrual cycle in which the ovarian follicle develops and matures. This half of the menstrual cycle begins on the first day of menses and ends with ovulation. The follicular phase is characterized by a gradual rise in the steroid hormone, estrogen. 

Follistatin is a protein that binds to the hormone activin. It is produced in the ovary and pituitary gland and is one of several proteins that regulate FSH secretion by controlling the activating hormone, activin.

Gamete intrafallopian tube transfer (GIFT) is an assisted reproductive technology. First, eggs are removed from the woman’s ovary, and a sperm sample is collected from the man. Then, the two are delivered via catheter to the woman’s fallopian tube, where fertilization will hopefully take place. This differs from IVF, in that the fertilization occurs in the woman’s body as opposed to inside a petri dish.

The gastrula is an early post-implantation embryo that develops from the blastula. It consists of three layers of cells: the ectoderm, mesoderm, and endoderm. The process of differentiation into three germ layers is called gastrulation.

Gelation is the transition of a liquid to a solid-like gel. Gelation occurs when a solution of dilute polymers is cross-linked into a network.

Proteins are the functional units in cells that are encoded within defined regions of DNA. These regions are called genes, and genes are inherited from parents. Humans contain ~20,000 protein-coding genes. Collectively, all the genes in an organism are referred to as a genome.

The external reproductive organs. This includes the penis and scrotum in males, and the vulva in females.

In gametogenesis, a germ cell nest is a collection of immature primordial follicles connected by intercellular bridges due to incomplete cytokinesis thus far in the process. It is thought that this early connection is important in avoiding the production of defective germ cells.

Germinal vesicle breakdown (GVB) refers to the dissolution of the nucleus of an oocyte that is arrested in prophase of meiosis I (the breakdown of the germinal vesicle). In this stage, the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation. The oocyte will arrest in meiosis II at the metaphase (MII) stage, where it stays until fertilized by sperm.

The gestation period refers to the length of time between conception and birth (in humans, this is 266 days, which is just short of nine months). The gestation period varies among different species.

A male reproductive disorder that is characterized by round-headed, acrosomeless sperm. Globozoospermia may result in male factor infertility. 

A gonad is a reproductive gland that produces ova (eggs) in females and sperm in males. Female gonads are ovaries, whereas male gonads are testes (testicles). Both organs also produce hormones.

Gonadotoxicity is the temporary or permanent damage to ovaries or testes after exposure to certain substances or drugs. Aggressive chemotherapy and radiotherapy used for the treatment of some cancers and autoimmune diseases are the most common causes of gonadotoxicity and subsequent infertility.

Gonadotrophin releasing hormone (GnRH) is a hormone secreted in pulses by the hypothalamus, which stimulates the synthesis of gonadotrophins by the pituitary gland. Gonadotrophins are essential for the development of ovarian follicles (FSH) and for ovulation (LH).

Growth hormone (GH) is a hormone produced by somatotropes and acts on the liver and adipose tissue to control growth, and the metabolism of lipids, proteins, and carbohydrates.

A gynecologist is a physician who focuses on the health care of women and, in particular, the female reproductive system.

When an organ or tissue pushes through a weak spot in the surrounding muscle or tissue. The most common type of hernia that is relevant to reproductive health is the inguinal hernia, which occurs in males when the intestine or bladder protrudes through the inguinal canal. 

A histone is a protein located in the nucleus of eukaryotic cells that organizes DNA into compact structures.

The term homologous refers to chromosomes that have the same pattern of genes.

Hormonal contraception or hormonal birth control refers to any medication or medical preparation that contains either estrogen or progesterone or a combination of the two hormones that a woman takes in order to prevent a pregnancy from occurring. Hormonal birth control is often prescribed to treat other medical conditions, as well, such as acne, heavy periods, and relief for the symptoms of PCOS, endometriosis, etc. Hormonal contraception may be taken orally, implanted, injected, absorbed via a patch on the skin’s surface, or placed inside the vagina. Hormonal contraception acts by either preventing the ovulation of a matured egg from the ovary each month, by making the cervix more difficult for the sperm to pass through, or by making the lining of the uterus less capable of supporting the implantation of an embryo.

Hormone (or endocrine) disruptors are substances that interfere with the proper functioning of the endocrine system (i.e., the production, release, transport, and regulation of hormones in the body). Classes of endocrine disruptors include synthetic chemicals found in the environment, plastics, pesticides, and various pollutants. Exposure to such substances has been linked to various pathologies in both animals and humans.

Hormone replacement therapy (HRT) is a medical treatment used to lessen the symptoms of menopause, such as hot flashes, night sweats, and vaginal dryness. Doctors may prescribe pills, creams, or skin patches containing the hormones estrogen or progesterone (alone or in combination) to mimic naturally-occurring levels of hormones produced by the ovaries prior to the onset of menopause.

Hot flashes (or flushes) are common symptoms of menopause characterized by a sense of significantly increased bodily temperature, rapid heart rate, perspiration, and a flushed appearance of the face. Hot flashes occur with great frequency in the early stages of menopause, from a few times per week to multiple times per day. Though most menopausal women experience hot flashes to some degree, it is possible to go through menopause without ever experiencing a hot flash.

Human chorionic gonadotropin (hCG) is a protein hormone produced by a developing embryo which stimulates progesterone production essential for the maintenance of pregnancy. It can be detected in maternal blood as early as 10 days after fertilization occurs. It is often used as a biomarker to detect pregnancy.

Hydrocephaly refers to a build-up of cerebrospinal fluid in the brain. This is dangerous, as the excess fluid increases pressure and can compress and permanently damage the brain. Hydrocephaly usually accompanies spina bifida and is often a result of obstructed flow of cerebrospinal fluid in the ventricular system before birth.

The hymen is a ring of tissue on the rim of the vaginal opening. This tissue can be torn during sexual intercourse or other means of penetration, such as tampon use during menstruation.

Hyperplasia is an increase in cell number in an organ or tissue, which could be an indication of abnormal or precancerous changes.

Hypoblast is the underside of the embryonic disk, which arose from the inner cell mass during the late blastula and early trophoblast stages of embryonic growth. These cells give rise to the yolk sac, the extra-embryonic tissue that will help support embryonic growth.

Hypoploidy is a state in which cells contain one or more fewer chromosomes than what is normal. Humans normally have 46 chromosomes per cell, but if a human has 45 or less chromosomes per cell, that person is hypoploid. One example of a hypoploid human disorder is Turner syndrome, where females have only one copy of the X sex chromosome.

A hysterectomy is the surgical removal of a woman’s uterus.

in situ is a term used as an intermediate between in vivo and in vitro. For example, examining cells within an organ removed from the body would be an in situ experiment, as the organ has been removed from its native environment (the body), but the cells are being studied in the context of their usual place within the organ.

in vitro fertilization (IVF) is an assisted reproductive technology procedure in which eggs are combined with sperm outside of the body, so that fertilization can occur. The embryos that are created can then be implanted back into a woman’s uterus or frozen (cryopreserved) for future use.

Incontinence is the inability to control urination or defecation.

Infertility is the inability to become pregnant after one full year of trying to conceive a child (or six months, if a woman is 35 years of age or older).

A passage in the anterior part of the abdominal wall which connects the abdominal cavity to the external genitalia. Structures such as the testes migrate through this pathway to enter the male scrotum. 

The inner cell mass (ICM) is the part of the blastocyst that is fated to become the embryo, amnion, and yolk sac. In contrast, the trophectoderm cells of the blastocyst will contribute to extra-embryonic tissues, such as the placenta and umbilical cord. Cells of the ICM are pluripotent, meaning they can give rise to all the cell lineages (ectoderm, endoderm, and mesoderm) found in the body. The ICM is, thus, a source of embryonic stem cells.

A term used to describe individuals whose reproductive organs or sex characteristics don’t match what is typically described as male or female. 

The term intrauterine refers to occurrences within the uterus. However, since the uterus has a cavity that is accessible through the cervix, the term is often used to mean "within the uterine cavity." Thus, intrauterine development refers to development of the embryo within the uterus (both before and after implantation), while an intrauterine device (IUD) is a contraceptive device inserted into the uterine cavity. 

Intrauterine growth retardation (or restriction) (IUGR) is the term applied to the condition resulting in a baby that is born of low birth weight (<10th percentile). It generally results from insufficient placental support.

A karyotype refers to the number and appearance (including physical structure, size, and banding pattern) of chromosomes in a cell.  To generate a karyotype, metaphase chromosomes are obtained from a population of dividing cells from virtually any cell or tissue (blood, amniotic fluid, blastomere, etc).  These chromosomes are spread onto a glass slide and stained with a dye specific for DNA that produces a characteristic banding pattern. The chromosomes are then imaged with a microscope and with the assistance of computer programs, chromosome pairs are identified and arranged in descending order of size.  Finally, the banding patterns of each chromosome are analyzed. This assists in the detection of genetic anomalies including chromosome structure defects or various aneuploidies.  For example, Trisomy 21 also commonly known as Down’s Syndrome, would be evident on a karyotype as three copies of chromosome 21 instead of only two that would be present in a euploid autosome or somatic cell.

The labia minora is a part of the vulva (the external portion of the female genital organs) and includes the two innermost folds of skin between the labia majora. The skin over the labia minora does not contain hair and surrounds the clitoris, urethra, and vaginal opening.

Lactotropes are specialized cells in the anterior pituitary gland that produce the hormone prolactin.

Laparoscopy is a key-hole surgical procedure that allows surgeons to see inside the abdomen. This type of surgery is very useful for viewing the female reproductive organs (uterus, ovaries, etc.). It normally requires a general anesthetic, but patients can often go home the same day as surgery.

Also known as Gregor Mendel’s second law, this law states that any given two traits are inherited independently of one another, and the probability that they are both inherited is left to chance.

A non-steroidal aromatase inhibitor. As this drug reduces estrogen production, it may be used to induce ovulation, and in the treatment of estrogen-sensitive of breast cancer.

Libido is a term for sexual desire or the degree of sexual appetite and is the psychological and emotional energy attached to one’s sex drive. Low libido is associated with a decreased desire to have sexual intercourse.

The luteal phase is the portion of the menstrual cycle in which the corpus luteum forms and matures. This half of the menstrual cycle begins with ovulation and ends when menstruation begins. The luteal phase is characterized by a gradual rise in the steroid hormone progesterone.

Luteinizing hormone (LH) is a hormone released by the pituitary gland that regulates a female’s menstrual cycle and ovulation. LH also plays an important role in a male’s sperm production, as it stimulates the production of male sex hormones.

The mammary gland is an organ unique to mammals that produces milk for feeding their offspring. In humans, the mammary glands are also called breasts.

Meiosis is a type of cell division that produces gametes (sperm and egg cells). Unlike regular somatic cells, which contain 46 chromosomes, gametes contain only 23 chromosomes.

Menarche is a woman’s first menstruation and occurs at an average age of 13 in the United States.

Menorrhagia refers to abnormally heavy bleeding and/or cramping during the menstrual period.

The menstrual cycle is the recurring cycle of physiological changes that occur in females and other primates of reproductive age. The menstrual cycle results from the coordinated actions of hormones made by the brain and pituitary gland acting on the ovaries and uterus in order to coordinate ovulation and fertilization. Hormones like FSH, LH, and activin made in the pituitary gland respond to and control the release of estrogen, progesterone, and inhibin by the ovary. These hormones then control and prepare the uterus for an egg, if fertilized. If the egg that is released each month is not fertilized, the uterine wall is shed. The shedding of the uterine wall is known as menstruation and is the more obvious external evidence of a functional reproductive cycle.

A membrane that supports an internal structure and attaches it to the wall of the body cavity. 

The mesentery of the uterus and the largest subsection of the broad ligament. 

A part of the broad ligament that serves as the mesentery of the fallopian tubes.

Metaphase is the stage of cell division during which chromosomes are aligned at the equator of the spindle. The cell is stalled in this stage until all chromosomes are properly aligned. This is known as the metaphase to anaphase checkpoint. Mistakes in aligning the chromosomes (e.g. lagging chromosomes) or in the metaphase to anaphase checkpoint can result in aneuploidy.

The sperm mid-piece is the part of the sperm tail closest to the head where the mitochondria are located. The mitochondria provide the sperm with energy as they travel through the female reproductive tract.

Mitochondria are organelles responsible for producing ATP, which is the cellular energy source. Additionally, they can synthesize steroids. Mitochondria are considered to be a semi-autonomous organelle because they replicate by self-division, have their own protein synthesis machinery, and have their own genome. Unlike the genome of the cell, which is inherited maternally and paternally, the mitochondrial genome is inherited only from the mother through mitochondria present in the egg at fertilization.

Monosomy is a form of aneuploidy and occurs when only one chromosome in a pair is present. All instances of monosomy are lethal except for Turner Syndrome.

Morphology refers to the shape and structure of a cell, tissue, organ, or organism.

Mosaicism exists when cells undergo changes during development such that one group of cells differs from a neighboring group. It can occur in both somatic and germ cells. Mosaicism can be caused by spontaneous DNA mutations (in either nuclear or mitochondrial DNA), spontaneous reversion of an existing DNA mutation, epigenetic changes in chromosomal DNA, and chromosomal abnormalities. Symptoms that occur as a result of mosaicism depends on the extent of the mosaic cell population. Mosaicism is important in terms of human disease. It also provides variations at the molecular level among humans, including between identical twins.

A mucus plug is present during pregnancy and is located at the cervix to block bacteria from passing into the uterus.

Mutagenesis is the process by which genetic mutations occur.

The myometrium is the middle layer of the uterine wall, consisting mostly of smooth muscle cells, with some vascular and stromal tissue. The myometrium contracts during menses and labor.

A condition in which all of the sperm in a fresh semen sample are dead.

Neo-oogenesis is the production of new oocytes throughout the lifetime of an organism. Neo-oogenesis commonly occurs in lower vertebrates (amphibians and reptiles), but is thought not to occur in higher vertebrates, especially mammals.

Neural tube defects (NTDs) are birth defects of the brain, spine, and spinal cord that usually occur during the first month or trimester of pregnancy, often before a woman realizes she is pregnant. This is why women of childbearing age are advised to take a multivitamin with 400 micrograms of folic acid a day, as this is proven to help prevent NTDs.

A highly conserved cell-cell signaling pathway that plays a major role in embryonic development. 

An obstetrician is a physician who focuses on the branch of medicine associated with pregnancy and childbirth.

Oligospermia is the medical term for a condition in which low numbers of sperm are present in the semen or ejaculate. Genetic, idiopathic, and iatrogenic factors can result in oligospermia. This condition often results in infertility, which can sometimes be overcome through the use of assisted reproductive technology.

An oncologist is a physician whose focus is cancer diagnosis and treatment.

An oocyte is a female germ cell that is not yet ready for fertilization. The oocyte matures into an ovum (egg) that will be released during ovulation.

Oogenesis is the production of oocytes, the female gamete. It is the female form of gametogenesis. Oogenesis begins early in development with the migration of primordial germ cells to the gonads. Oogenesis is unique in that it is halted midway through the process and does not resume until fertilization occurs. 

An oophorectomy is the surgical removal of one or both of a woman’s ovaries.

An orgasm refers to the peak of physical response to sexual stimulation characterized most often by intense pleasure, involuntary muscular contractions of the lower pelvic region, and ejaculation (possible for both men and women). Orgasms are controlled by the limbic system, a set of structures in the brain, including the hypothalamus, which plays a role in sexual response.

An osteoclast is a large, multinucleate cell that exists in growing bone and breaks down bony tissue.

Osteoporosis is a loss of bone density that can result in increased risk of fractures and structural body deformities. It is defined as a bone mineral density greater than 2.5 standard deviations below the mean bone mineral density of young, healthy adults. Because estrogen is important in the maintenance and remodeling of bone, post-menopausal women naturally lose bone density with age and are at increased risk of osteoporosis.

The ovarian cortex is the outer layer of the ovary consisting of stroma, located just inside the tunica albuginea. The ovarian follicles are contained in the cortex.

Ovarian hyperstimulation is an assisted reproductive technology in which fertility medications are used to induce the ovaries to grow multiple follicles and eggs in a single cycle. In addition to the woman having more eggs released than normal (usually one egg per menstrual cycle), she experiences much higher hormone levels, particularly estrogen released from the growing follicles. In some cases, the supraphysiologic levels of hormones may trigger an exaggerated response, resulting in ovarian hyperstimulation syndrome. The syndrome has a broad spectrum of clinical features ranging from a mild illness needing only close observation to a severe illness with cardiovascular collapse requiring hospitalization and intensive care treatment.

The ovarian reserve refers to the fixed number of primordial follicles that is established prior to birth in humans. In the absence of neo-oogenesis, the ovarian reserve dictates a female’s reproductive lifespan. Factors, including various chemotherapeutics, which deplete the ovarian reserve can result in premature ovarian failure and the early onset of menopause.

Ovarian transposition is the process by which surgeons move the ovaries away from the area receiving radiation therapy. The goal of the surgery is to move the ovaries within the pelvis where they can still function but will be out of the way of harmful radiation. This technique will not protect against the effects of chemotherapy.

The ovary is one of two female reproductive organs that produce eggs and release hormones, like estrogen.

Ovulation is the process in which an ovarian follicle bursts, and the mature egg is released from the ovary into the fallopian tube. Ovulation usually occurs halfway though a woman’s menstrual cycle and marks the transition between the follicular and luteal phases.

A Pap smear is a method to screen for cervical cancer. Squamous cells (flat, scale-like cells) are obtained from the outer surface of the cervix as well as columnar cells (tall, thin cells) from the inner canal leading to the uterus. The junction where these two cell types meet is called the transformation zone and is where most cell abnormalities are found.

Parthenotes are the products of parthenogenesis, the process in which eggs become activated to begin dividing without fertilization. Parthenotes contain genetic material from only the maternal source. In contrast, embryos are created through fertilization and contain genetic material from two genetically distinct cells. No viable human parthenote has been reported.

A group of muscles located in the lower abdomen that support the surrounding organs including the reproductive organs, the bladder and the bowel. 

The pelvis is the basin-shaped structure of the vertebrate skeleton that supports the upper torso and spine and protects the rectum, bladder, and reproductive organs.

Perimenopause, also called the "menopausal transition," is the time frame in which a woman's body shifts from regular cycles of ovulation and menstruation to menopausal symptoms, including hot flashes, vaginal dryness, night sweats, absence of menstruation, and permanent infertility. This period typically begins when women reach their 40s, though symptoms can be detected earlier.

In females, the perineum is the area between the vagina and anus, and in males, it is the area between the scrotum and anus. The perineum is considered to be an erogenous zone in both sexes, and the female perineum is highly susceptible to damage during childbirth.

A pharmacological chaperone (or pharmacoperone from "protein chaperone") is a small molecule that enters cells and serves as a molecular scaffolding in order to cause otherwise-misfolded mutant proteins to fold and route correctly within the cell. Mutation of proteins often causes molecular misfolding, which results in protein misrouting within the cell. Accordingly, mutant molecules may retain proper function but end up in parts of the cell where the function is inappropriate, or even deleterious, to cell function. Misfolded proteins are usually recognized by the quality-control system of the cell and retained (and often destroyed or recycled) in the endoplasmic reticulum. Pharmacoperones correct the folding of misfolded proteins, allowing them to pass through the cell's quality-control system and become correctly routed. Since mutations often cause disease by causing misfolding and misrouting, pharmacoperones are potentially therapeutic agents, since they are able to correct this defect.

Ref.: Conn, P.M. and Janovick, J.A., A New Understanding of Protein Mutation Unfolds, American Scientist 93:314-321, 2005.

The pituitary gland is a very small organ, located at the base of the brain, which produces and releases hormones (signals) that control other organs and body processes. The pituitary gland responds to signals from the hypothalamus. The anterior pituitary gland is the front portion of the pituitary gland, and it secretes hormones that control physiological processes including growth, reproduction, and stress. The posterior pituitary gland is behind the anterior portion and secretes hormones involved with water balance and uterine contractions during labor.

A polar body is the product of asymmetric cell division that occurs during meiosis. Both phases of meiosis produce a polar body, and the final result of completed meiosis is two polar bodies and one haploid egg. The formation of polar bodies allows the DNA content of the egg to be reduced while still maintaining critical stores of maternal components in the egg that are important for supporting future fertilization and pre-implantation embryo development.

Polycystic ovary syndrome is a common hormonal disorder that affects many women of reproductive age. The name of the disorder came from the observation that women with PCOS often have the appearance of “cysts” along the outer edge of their ovaries when viewed by ultrasound. These “cysts” correspond to immature follicles that have stopped developing due to hormonal imbalance. Polycystic ovaries develop as a consequence of excess ovarian androgen. PCOS can disrupt ovulation or stop it altogether, often leading to subfertility. Women with PCOS may experience excessive hair growth, weight gain, acne, and many other symptoms, ranging from mild to severe.

A polymer is a large molecule composed of repeating structural units. Polymers may be natural (e.g. DNA or alginate) or be synthetic (e.g. plastics).

Polyspermy occurs when more than one sperm enters the egg during fertilization. Polyspermy results in a zygote that contains too much DNA (polyploidy) and that is often non-viable. During normal fertilization, the egg has several mechanisms to prevent this from occurring, including the block to polyspermy established by the zona pellucida.

Post-implantation refers to the time of embryo development that occurs after implantation in the uterus has occurred.

Postnatal refers to occurrences after giving birth.

The period of time immediately following childbirth. This period can be divided into three distinct yet continuous stages. The first 6-12 hours postpartum a woman is said to be in the initial/acute phase, during which time the mother must be carefully monitored for post pregnancy complications such as hemorrhage, eclampsia and embolism. Following this, a woman enter the subacute phase, which last for 2-6 weeks. This phase is characterized by rapid changes that attempt to return the female body to its normal, nonpregnant state. The third phase of the postpartum period, the delayed period, may persist for up to 6 months after childbirth. During this time, the female body gradually recovers from giving birth.

An ovarian follicle that has no antrum during folliculogenesis. Most growing follicles at the early stages of folliculogenesis are preantral follicles. Preantral follicles consist of ocytes, granulosa cells, and theca cells, which grow and mature during folliculogenesis. 

In humans, pregnancy refers to the development of offspring (either a single offspring or multiple) in the uterus of a woman in preparation for the birth of independent human life.

Preimplantation genetic diagnosis (PGD) is an ART procedure in which genetic testing is done on biopsied cell(s) from a preimplantation-stage embryo. With this technology, only unaffected embryos are transferred back to the recipient uterus to initiate a pregnancy. PGD was originally developed to screen for single gene disorders but is currently used to detect different factors, including HLA-type, chromosome abnormalities, and aneuploidy. Genetic testing can be done on biopsies of the first or second polar bodies, a single blastomere from a cleavage-stage embryo, or several trophectoderm cells from a blastocyst.

Premature ovarian failure (POF) is also referred to as premature menopause or primary ovarian insufficiency, and it is characterized by the inability to ovulate and an early loss of function of the ovaries altogether due to a lack of or no follicles in the ovary in women who are under the age of 40 (prior to the typical onset of menopause). POF leads to subfertility or infertility and is also linked to osteoporosis and other autoimmune disorders. It can be a result of genetic abnormalities, removal of the ovaries, or prior radiation therapy or chemotherapy. Premature ovarian failure differs from menopause in that women with premature ovarian failure may have occasional or irregular periods and may possibly become pregnant.

Prenatal refers to occurrences during pregnancy (before giving birth).

The primary germ layers are the ectoderm, mesoderm, and endoderm. Primordial germ cells are typically considered distinct from primary germ layers, although all are derived from the inner cell mass of the embryo.

the earliest recognized gamete precursors. During embryonic development, these cells arise from the epiblast and migrate to the gonads, which they then populate. Eventually, through the process of maturation, these cells become functional gametes. 

Progesterone is a steroid hormone released by the corpus luteum and placenta that prepares the uterus to receive and support a fertilized egg. It is the predominant hormone secreted during the luteal phase of the menstrual cycle and is essential in establishing and maintaining a pregnancy. 

Prolactin (PRL) is a hormone released by the pituitary gland. It primarily acts on the mammary gland to initiate and maintain milk production after pregnancy.

Prophase is a phase of cell division during which DNA is packaged and condensed into chromosomes.

Prostate specific antigen (PSA) is a protein produced by the prostate which facilitates sperm motility in semen. It is used as a biomarker to detect prostate enlargement or prostate cancer.   

Recombination is the exchange of genes between chromosomes (typically by crossing-over) that occurs during the production of gametes and results in a unique combination of genetic material. Recombination allows for the introduction of genetic variation and is a key aspect of sexual reproduction.

A regimen is a plan of health maintenance, often with respect to diet, therapy, and/or general prescribed treatment.

Relaxin is a protein hormone produced by the corpus luteum of the ovary, as well as other male and female reproductive organs. It is thought to play important roles in preparing the reproductive tract for birth and the changes that occur in the mother's cardiovascular system during pregnancy. Loss of relaxin in pregnant female mice results in an inability to feed their newborn pups due to impaired nipple development.

A subspecialty of obstetrics and gynecology (OBGYN) which focuses on the treatment of infertility. An REI specialist may use a combination of surgerys, procedures, and medicine in attempt to help a couple achieve pregnancy. These specialists are sometimes referred to as “infertility doctors” or “fertility specialist."  

A uterus that tilts posteriorly at the cervix

A technique which involves the injection of a round, immobile spermatid into an oocyte in attempt to achieve fertilization and eventually, pregnancy. This technique may allow males who do not produce fully mature sperm to become biological fathers. 

A secondary ovarian follicle is a maturing ovarian follicle consisting of an oocyte surrounded by two or more layers of tall, supporting granulosa cells.

Semen is the fluid expelled during ejaculation, usually at the point of orgasm. Semen contains sperm and the secretions of the seminal vesicles, as well as the prostate and bulbourethral glands.

The seminiferous tubules in the testes are the location of sperm cell differentiation and development.

Sex refers to the differences in physiology and biology between women and men, such as chromosomal differences (xx versus xy) and genitalia appearance/function. Sex is also a term used to describe the physical acts of intimacy performed between individuals, which can include (but are not limited to) sexual intercourse, caressing, and oral stimulation.

A gene found on the Y chromosome that encodes for the testis determining-factor protein which induces male sex determination

Sexual reproduction is the process in which the male gamete (sperm) and the female gamete (egg) fuse to create a genetically distinct offspring.

A sexually transmitted infection (STI) or a sexually transmitted disease (STD) is an infection that is transmitted through intimate sexual acts, such as anal, vaginal, or oral sex, or simply by genital contact.

Sister chromatids are identical copies of a chromosome joined together by a centromere.

Social egg freezing (or social oocyte cryopreservation) is a form of fertility preservation that allows healthy women to freeze their eggs (oocytes) for use in the future. The procedures and techniques are the same used in conventional egg freezing performed for cancer patients. Egg freezing procedures include the use of injectable hormones to stimulate the ovaries to promote the growth of multiple mature eggs, a surgical procedure to collect oocytes from the ovary, rapid freezing of mature oocytes, and the storage of cryopreserved oocytes for a period of time (e.g. years). In the future, these oocytes can be thawed and used for in vitro fertilization by sperm to create embryos, which can then be transferred into the uterus to achieve pregnancy. Social egg freezing is generally accepted in the United States, although it is prohibited in many countries.

Somatic cells are diploid cells that make up all organs and tissues within an organism. In contrast, germ cells (or gametes) and stem cells within an organism are not somatic cells.

The sperm (spermatozoon) is the male reproductive cell that carries the paternal (father’s) haploid genome. Each sperm cell consists of a head (containing the sperm nucleus), a midpiece (containing mitochondria), and a flagellar tail. Spermatozoa are fully formed when they leave the testis but must undergo additional maturation processes in the epididymis and female reproductive tract (capacitation) before they are capable of fertilizing an egg.

Sperm donation refers to the act of a man (the sperm donor) providing his sperm to another infertile man or couple having difficulty conceiving their own biological child in the hopes of allowing them to become pregnant. Sperm donation is part of the process of third–party reproduction. Sperm donation is typically facilitated through a sperm bank or clinic and can occur either privately or openly with the intended mother or recipient couple. Pregnancies using sperm donations are typically achieved using artificial insemination rather than in vitro fertilization.

A spermatid is a haploid male germ cell that has completed the process of meiosis. Immediately after meiosis, spermatids are round cells that do not resemble mature sperm. Round spermatids must go through the process of spermiogenesis in the testis to form structures, such as the head, tail, and acrosome and to become elongated spermatids.

Spermatogenesis is the process by which male gametes (spermatozoa) are formed in the seminiferous tubules of the testis. Spermatogenesis consists of three phases: mitotic division of the spermatogonia (proliferation), meiotic division of the spermatocytes to produce spermatids (meiosis), and differentiation of round spermatids to form elongated spermatids (spermiogenesis). Germ cells remain in contact with Sertoli cells throughout spermatogenesis. After spermatogenesis in the testis, spermatozoa are still immotile and must go through further maturation processes in the epididymis and female reproductive tract before they are able to fertilize an egg.

Spermiogenesis is part of the process of spermatogenesis (they are not the same thing). During spermiogenesis, haploid, round spermatids change their shape and structures to become elongated spermatids and acquire the specialized parts needed to become mature sperm.

The modification of spiral arteries in the maternal decidua which is necessary for the establishment of a maternal vascular system that can adequately support the fetus.

Steroid hormones are natural hormones produced in the adrenal glands, testes, and ovaries (and in the placenta during pregnancy). There are five major classes of steroid hormones that are derived from the same cholesterol precursor: 1) androgens, 2) estrogens, 3) progestins, 4) mineralcorticoids, and 5) glucocorticoids. Androgens and estrogens function in sexual development, differentiation, and the development of secondary sex characteristics and behaviors. Progestins act to regulate the menstrual cycle and pregnancy. Mineralcorticoids and glucocorticoids do not have established functions in reproduction but do influence a wide variety of vital biological functions.

Subfertility refers to decreased fertility but not a complete inability to become pregnant. Some common causes of subfertility in women include ovulatory disorders, such as premature ovarian failure (POF) and polycystic ovarian syndrome (PCOS), or uterine abnormalities, such as endometriosis. Subfertility also occurs with advanced female age.

Surrogacy is an arrangement in which a woman carries and delivers a child for another couple or person. Surrogacy may be traditional or gestational. Traditional surrogacy is the treatment in which a third-party woman carries an embryo created after artificial insemination in her uterus. In this case, the third-party woman has a genetic link to the fetus she might carry and deliver. Gestational surrogacy (using a gestational carrier/uterine carrier) is the treatment in which a third-party woman carries an embryo created after in vitro fertilization in her uterus. In this case, the third-party woman has no genetic link to the fetus she might carry and deliver.

Syngamy is the permanent fusion of two individual cells (or gametes) to produce a unique organism (the zygote). This is also called sexual reproduction or fertilization.

Telophase is the stage of cell division following anaphase during which chromosomes have been pulled to each spindle pole. New nuclei begin to form, and chromosomes begin to unravel.

Teratospermia is the medical term for a condition in which sperm with abnormal morphology are present in the semen or ejaculate. Typically, more than 40% of the sperm in the semen will have abnormal morphology, including small sperm, large sperm, and sperm with defects in the head, tail, and/or mid-piece. The causes of teratospermia are largely unknown. This condition may result in infertility, which may be overcome through the use of assisted reproductive technologies.

Testicular tissue banking is the process in which testicular tissue, including cells that produce sperm and sperm itself, is removed and frozen.

A transcription factor encoded by the SRY gene that causes the bi-potential gonad to proceed down a male-specific pathway.

Thalidomide was an over-the-counter drug used by pregnant women experiencing morning sickness in late 1950s Germany. Unfortunately, thalidomide caused severe birth defects in the children of the women who took the drug while pregnant, and many of these children did not survive. This catastrophe highlighted the need for more stringent drug-testing regulations. Now, the drug is only available by prescription for the treatment of cancer, leprosy, etc.

Third-party reproduction refers to the use of donor eggs, sperm, embryos, or the use of a surrogate mother or gestational carrier to allow an infertile person or couple to become parents. Donor eggs and sperm can be used in assisted reproductive technology procedures such as in vitro fertilization or artificial insemination to produce an embryo(s). Donor embryos or embryos derived from the biological parents can then be placed in the uterus of the future mother or gestational carrier. The third party’s involvement is typically limited to the reproductive process and does not extend to parenthood.

The thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are produced by the thyroid glands and are mainly responsible for growth and metabolism.

Thyrotropes are specialized cells in the anterior pituitary gland that produce thyroid stimulating hormone (TSH).

Transdermal therapy is a form of treatment where medication is delivered through the surface of the skin and into the bloodstream. Transdermal therapy can be administered in the form of a transdermal patch, lotion, or gel and is often used to deliver hormones for the purpose of contraception or to treat the symptoms of menopause.

A transgene is a gene or genetic material that is artifically added into an organisms's genome. Transgenes are used by genetic engineers to change or insert genes of interest into an organism. They are often associated with a phenotype, making them very useful for biomedical research studies.

A type of ultrasound which utilizes a transducer that is inserted into the vagina to view the pelvic organs and reproductive tract.

A trimester is a three-month stage of pregnancy. Classically, pregnancy is nine months (40 gestational weeks) and is divided into three trimesters: the first trimester is the first three months (1-12 gestational weeks), the second trimester is the middle three months (12-28 gestational weeks), and the third trimester is the last three months (28-40 gestational weeks).

Trophoblasts are a heterogeneous population of cells derived from the trophectoderm (the outer cell layer of the blastocyst) that mediate and contribute to the construction of the connection between the mother and fetus at the site of implantation (the placenta). There are considerable species differences in terms of trophoblast differentiation. In humans, the differentiated forms are cytotrophoblasts, syncytiotrophoblasts, and extravillous trophoblasts.

A disease characterized by blocked or damaged fallopian tubes. Tubal disease can prevent fertilization and implantation from occurring, and is therefore a leading cause of female infertility.

Tumor necrosis factors (TNFs) are a family of cytokines (signal molecules) which signal by binding to two specific receptors, TNF-receptor type I and TNF-receptor type II. Activation of the TNF signaling pathway controls cell survival, death, proliferation, and differentiation. This pathway, therefore, is responsible for the development, organization, and homeostasis of many tissues, including the breast and brain/nervous system.

The umbilical cord is a thin organ that connects the fetus to the placenta while in utero. The umbilical cord contains two arteries and a vein that facilitates oxygen and nutrient transport to the fetus. It also transports fetal waste back to the placenta to be filtered in the maternal circulation.

A urinary tract infection (UTI) is an infection caused by bacteria that occurs in the urinary system (kidneys, ureters, bladder, and the urethra). Symptoms are often uncomfortable and can include pain or burning upon urination, fever, and fatigue.

The uterine glands are in the epithelial, glandular compartment of the endometrium, which is contiguous with the luminal epithelium. The glands synthesize and secrete most of the proteins and other components of uterine fluid (histotroph). Glandular secretions are necessary for embryo implantation and survival.

Uterine leiomyoma is a benign tumor that originates from the smooth muscle layer (myometrium) of the uterus. It is also known as a uterine fibroid. Fibroids are the most common benign tumors of the female genital tract. While fibroids can be asymptomatic, they can also cause irregular or heavy vaginal bleeding and other symptoms due to pressure on neighboring organs.

Vaginal atrophy is the thinning and inflammation of the vaginal walls due to declining estrogen levels. This condition typically occurs post-menopause, but it can also occur during breastfeeding or at other times when the body’s estrogen levels are lower than usual. Symptoms include painful intercourse, vaginal burning, dryness, painful urination, and urinary tract infections.

The vas deferens is a duct of the male reproductive system that connects the testes to the urethra. It runs from the end of the epididymis toward the prostate, where it joins with the seminal vesicle to form the ejaculatory duct. The vas deferens functions in the transport of mature spermatozoa and secretes a fluid that is a component of semen.

The vitelline membrane is a structure that directly surrounds the oocyte in lower organisms, such as insects, mollusks, amphibians, and birds. Its functional homologue in mammals is the zona pellucida.

The vulva is the external portion of the female genital organs. It includes the labia (majora and minora), clitoris, and the openings to both the vagina and urethra.

The withdrawal method refers to pulling the penis out of the vagina and away from the woman’s external genitals before the moment of ejaculation in order to prevent a pregnancy from occurring. However, this method of birth control is not highly effective, as sperm can reside in pre-ejaculation fluid. Also, this method does not prevent against any STIs.

The Wolffian ducts are paired, mesodermal ducts present in the early embryo that will develop into the epididymis, vas deferens, and seminal vesicles in males. In females, they are lost during the early stages of development.

The yolk sac is a pouch-like tissue in the early embryo that lies adjacent to the embryonic hypoblast portion of the developing inner cell mass. Its earliest stage during implantation in the mammal is derived from the blastocyst cavity and is termed the primary yolk sac. This is followed by the development of a secondary yolk sac, which develops within the primary yolk sac and displaces it; the secondary yolk sac is derived from the cells of the hypoblast. As development proceeds, the yolk sac is partially incorporated into the tissues of the intestines. Early in mammalian gestation and throughout gestation in other animals, the yolk sac serves as the reservoir for stored lipids, fats, and proteins, and it is also the site of early production of blood. Stem cells for both germ cells and hematopoietic cells reside within the yolk sac, close to the embryo, and migrate into the embryonic abdomen early in gestation. The yolk sac is resorbed into the embryo abdomen at varying times across species (e.g. it is still present at the time that hatching occurs in fish and amphibians and has been resorbed in birds, while in mammals, resorption takes place mid-gestation).

The zona pellucida is a membrane composed of four glycoproteins (ZP1-4) that surrounds the plasma membrane of the mammalian oocyte. It is important for inducing the acrosome reaction during fertilization and preventing polyspermy. The zona pellucida persists through pre-implantation embryo development, but the blastocyst must hatch out of the zona pellucida in order to undergo implantation in the uterus.