A Reproductive Lexicon


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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.

Oncofertility is a new discipline that bridges oncology and reproductive medicine in order to discover and apply new fertility preservation options for young patients facing fertility-threatening diseases or treatments.

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

Oncology is the field of medicine that focuses on cancer.

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. 

Female germ cells with diploid and stem cell characteristics that can self-proliferate and differentiate (in invertebrate and some lower vertebrate species). OSCs produce new female oocytes through oogenesis during the life-cyle of reproduction. In mammals, the existence of OSCs has been debated.

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

Oophoropexy or ovarian transposition is a surgical procedure in which one ovary or both ovaries are either suspended (disconnected from the uterus) or undergo fixation, a procedure in which the ovary is elevated and fixed to the abdominal wall. Patients requiring radiation therapy may undergo oophoropexy via laparoscopy prior to the first radiation treatment, where their ovaries are repositioned in the abdominal cavity away from the radiation field, reducing exposure to radiation.

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.

Osteopenia is a condition in which the bone mineral density is low when compared to normal levels but not low enough to qualify as osteoporosis.

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.

Ovarian cancer is a cancer of the ovaries, the female reproductive organs that produce eggs and release hormones.

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.

The ovarian follicle is the functional unit of the ovary composed of an oocyte surrounded by companion somatic cells, including granulosa cells and theca cells. The somatic cell component of the follicle produces hormones important for oocyte development and proper endocrine function. Communication between the granulosa cells and the oocyte, which are mediated by transzonal projections, is essential for proper oocyte growth during oogenesis. The fully-grown oocyte is released from the follicle in response to hormonal cues at the time of ovulation.

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.

Ovarian protection methods are various surgical and non-surgical methods used to reduce the risk of ovarian damage during chemotherapy and radiotherapy. Surgical protection is a prophylactic transposition of the ovaries away from the field of pelvic irradiation (oophoropexy), while non-surgical protection includes pelvic shielding and the use of GnRH analogues and fractionated doses of chemotherapy and radiotherapy.

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 tissue banking is the process in which one entire ovary (or part of an ovary) is removed surgically, and the outer surface (cortex), which contains the eggs, is frozen in strips for later use. Women who are survivors of some types of cancer can have pieces of the tissue thawed and transplanted back into the body. A number of pregnancies have resulted from using this technique. Transplantation is not always safe following some types of cancer (e.g. leukemia) because of the risk of re-seeding the original cancer. The Oncofertility Consortium® is actively researching new ways to use this tissue. New techniques are still experimental but may be the best option for women who must begin their treatments immediately.

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.

The oviduct is a structure that leads from the ovaries to either the uterus or outside the body, depending on the species. In mice, eggs are ovulated from the ovary into the oviduct where fertilization occurs. The fallopian tubes are analogous to the oviducts in humans.

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.

The ovum, also known as the egg, is the female reproductive cell or gamete. Eggs are arrested at metaphase of meiosis II, and following ovulation, they can be fertilized in the presence of sperm. In addition to containing DNA, the egg contains critical stores of maternal mRNAs and proteins that will support fertilization and subsequent embryo development.