The nulliparous cervix is approximately 2 cm in length. Its columnar epithelium is pierced by the ducts of mucous secreting glands which spew forth their contents as a protective barrier preventing bacteria from entering the upper reproductive tract and as a welcome channel to lead sperm into the upper tract. Cervical mucus is comprised of hyaluronic acid micelles which are affected by the hormonal milieu exposed to the glands. Late in the follicular phase, as estrogen rises, the micelles align in a parallel arrangement forming channels to guide the sperm. Under the microscope this can be seen as the classic "fern" pattern of dried cervical mucus (Figure 3). The pH is alkaline and nourishing to the sperm. Indeed, sperm can live in normal cervical mucus for as long as 4 days. The abundant mucus frequent oozes from the cervical os into the vagina to lure the sperm from the ejaculate, while protecting them from the acidity of the vagina. At midcycle, just prior to and after ovulation the rising progesterone increases the salt content of the mucus, breaking the micelle channels and thickening the consistency of the mucus. The "fern" pattern is no longer seen; the mucus thickens and becomes hostile to sperm and bacteria alike.
Women with a history of cervical infections, surgery or cryotherapy may have damage to the cervical glands and lack mucus. This may result in the inability of the sperm to survive the harsh vaginal acidity and not make the assent to the uterus. However, a considerable amount of cervix must be removed or damaged for a true "cervical" factor to causes infertility.
Infections rarely result in cervical infertility. Although gonorrhea and chlamydia have often been accused, it is difficult to prove that either of these actually destroys cervical glands and are more likely to result in tubal factor infertility (14). Acute infection may alter cervical pH, killing sperm, although this is not well documented.
Cervical conization which removes the cervical glands is the most likely cause of cervical factor infertility. Cryotherapy and laser vaporization may destroy the lower canal, but glands above the point of metaplasia usually provide enough mucus to retain fertility (15).
The normal squamocolumar junction with clear cervical mucus almost always rules out a cervical factor. When the cervix is scarred with a narrow external os and almost flush with the vagina, the cervical glands are frequently absent.
This diagnosis of cervical factor is based heavily of the history of cervical damage by surgery or infection. Nonetheless, the classic diagnosis of cervical factor infertility is made by the post coital test. However, the evidence of a poor post-coital associated with infertility is quite poor due to the wide variation in techniques and results (16). Thin or absent mucus with any moving sperm on the day of the urinary LH surge is strongly suggestive of cervical factor infertility. However, without a history of cervical damage by infection or surgery, this diagnosis is largely circumstantial.
A true cervical factor is best treated with intrauterine insemination as described below. Briefly, washed sperm are injected into the uterus at the time of ovulation. Because the sperm survive a limited time, it is probably best to time ovulation with urinary LH to narrow the insemination-ovulation interval.
In addition, prior cervical surgery may predispose to an incompetent cervix during pregnancy (17). Thus, the patient should be closely monitored for painless dilation of the cervix during pregnancy and evaluated for cervical cerclage.