Infertility is defined as the inability of a couple to conceive after one year of unprotected intercourse. This reflects how complicated even normal conception is.

Many factors can affect fertility, including the presence of sperm and egg at the right time in a receptive environment. Tests can evaluate these different aspects of fertility.

Male infertility is diagnosed by a semen analysis. A sample is studied with a microscope to determine the number of sperm, the appearance of the sperm, and the ability of the sperm to move. A low sperm count decreases fertility.

The female is tested for egg production by a combination of tests. One looks at the menstrual cycle's regularity because this is a good predictor of normal ovulation. The blood level of progesterone can also be measured during the month, along with basal body temperature. Both increase in the second half of the cycle if ovulation has occurred.

Because the sperm and egg must be able to meet in the woman's genital tract, tests check to see if the tract is open and intact. The hysterosalpingogram is an X-ray study of the cervix. A dye is injected that outlines the contours of the uterus. This shows if the fallopian tubes are open or blocked. Hysteroscopy, in which a fiber optic telescope is inserted through the vagina and cervix, allows for a visual evaluation of the uterine cavity.

Intra-abdominal conditions, most notably endometriosis, can impair fertility. With a pelviscopy, a small telescope is placed into the pelvic cavity through the abdominal wall. This lets doctors look in the pelvic and abdominal cavities for endometriosis, scar tissue and other problems.

Despite the variety of tests available, about one-third of infertile couples will have normal results. Their infertility remains unexplained.