Sperm must swim in the cervical mucus traveling from the vagina through the cervix and into the uterus. Small glands that line the cervix produce cervical mucus. The mucus must provide nutritional support for sperm and be of the correct consistency. Too little or "sticky" mucus can interfere with sperm transport causing infertility.

When estrogen levels increase prior to ovulation it causes increased mucus production and the mucus becomes "watery" thus enhancing sperm movement. Certain medications, such as Clomid can adversely affect the mucus by causing it to thicken.

Sometimes antisperm antibodies are found in the cervical mucus. These are antibodies produced by the female that mistake sperm for invading pathogens. When these antibodies are present numerous "dead" or immobile sperm are seen in the post coital test. Rarely, a man will produce antibodies to his sperm.

Cervical factor infertility is often treated via intrauterine insemination (IUI). Using this procedure, specially prepared sperm are inserted directly into the uterus using a small catheter. This avoids exposure of the sperm to the cervical mucus and insures it reaches the uterus.