Part of “CHAPTER 103 – THE DIFFERENTIAL DIAGNOSIS OF FEMALE INFERTILITY“

Several requirements must be met for pregnancy. The male partner must produce adequate numbers of normal, motile spermatozoa; the man must be capable of ejaculating the sperm (i.e., patent ductal system); and the sperm must be able to traverse the female reproductive tract (i.e., no obstruction of the female tract). The female partner must ovulate and release an ovum; the sperm must be able to fertilize the ovum; the fertilized ovum must be transported from the distal fallopian tube, the site of fertilization, to the endometrial cavity in a timely manner; and the fertilized ovum must be capable of developing into an embryo and implanting.

Normally, several million to several hundred million spermatozoa are deposited in the posterior vagina during coitus. There, the ejaculate forms a gel that undergoes liquefaction within 20 to 30 minutes of its formation. Even before liquefaction, sperm gain entry to the upper female reproductive tract through the cervical mucus. Most of the sperm in the ejaculate that remains in the vagina are immobilized rapidly and killed in the acidic milieu. Fewer than 200 sperm per ejaculate ever reach the distal oviduct.

Cervical mucus is a relatively impermeable barrier to sperm throughout the menstrual cycle except during the periovulatory period, when access to the upper reproductive tract is permitted. During this interval, estrogen induces several clinically recognized changes, including an increase in the amount of cervical mucus; a decrease in its viscosity, manifested as increased spinnbarkeit (i.e., elasticity); a decrease in cellularity; and a prominent ferning pattern when dried on a slide. The ultrastructure of cervical mucus alters; the fibrous strands become oriented into channels through which the sperm travel into the endocervix and endocervical crypts. After ovulation, the mucus undergoes a progesterone-mediated change that renders it impenetrable again.