Infertility, inability or diminished ability to produce offspring. Infertility affects about 15% of couples in the United States and the United Kingdom. Male fertility depends on adequate production of sperm by the testicles, unobstructed transit of sperm through the seminal tract, and satisfactory depositing of it within the vagina. Causes of impaired spermatogenesis include certain environmental poisons, undescended testicles, injury- or infection-related testicular atrophy, drug effects, prolonged fever, and endocrine disorders. Obstruction of the seminal tract may result from congenital defects and from inflammation of the testicles, epididymis, vas deferens, and prostate gland, and seminal surgical division of both vasa deferens (vasectomy). Defective delivery of sperm into the vagina may result from surgery of the bladder neck, removal of the prostate gland, hypospadias, premature ejaculation, functional or organic impotence, or structural abnormalities of the female genital tract.
Female infertility first of all depends on the ability to develop ova (eggs) in the ovaries. These eggs must be able to leave the ovaries and travel into and down the fallopian tubes. For sperm to be able to reach them, the structure of the vagina, cervix, and the main body of the uterus must not impair them, and the mucus surrounding the cervix must be abundant, clear, and elastic. The fallopian tubes must be clear, from the uterus up to the place where the sperm meet the eggs. In addition, after conception has occurred, the lining (endometrium) of the uterus must be able to take the implantation of the fertilized egg; otherwise, there will be an early miscarriage. Infertility in women can result from disease, disturbance, or deformity of any of these structures or functions. The most common reason for infertility is hormonal imbalance that affects the woman's ability to produce viable eggs or the type of cervical mucus that she produces. The fallopian tubes can become blocked by scars due to inflammation. There also may be some abnormality of the vulva, cervix, or uterus.
See also: Reproduction.