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.