Cervical mucus and the myth of the post coital test

Cervical mucus and pregnancy

Normally, mucus in the cervix (the lower part of the uterus that opens into the vagina) is thick and impenetrable to sperm until just before release of an egg (ovulation). As the egg develops in the ovary, estrogen is produced. The estrogen will gradually change the mucus so that it becomes clear and watery. As a result, sperm can move through the mucus into the uterus more easily. In the past, it was thought that if the mucus did not change at ovulation, that pregnancy would be unlikely to occur.

Impact of medications on cervical mucus

Clomid is a commonly used fertility medication. It works by interfering with estrogen and estrogen’s function. Because the production of cervical mucus is an estrogen dependent function, some women may notice a decrease in the amount of cervical mucus or cause it to remain thick and viscous instead of becoming watery at the time of ovulation. Although this effect has been observed, there is no evidence to support the theory that this reduced the chance for pregnancy compared to women taking Clomid whose cervical mucus remained normal.

In previous years, fertility doctors would prescribe women with “poor” or thick cervical mucus various types of estrogen in an effort to improve the cervical mucus. There is no evidence that any of these interventions improved the chances for pregnancy.

Post coital test – What is it?

In the past, fertility doctors would perform an examination called the post-coital (after intercourse) test. This test was developed as an attempt to “measure” whether sperm were able to swim through a woman’s cervical mucus in order to enter the uterus.  It was apparently first performed in 1866 by J. Marion Sims and later described by Max Huhner, thus it has also been called Sims-Huhner Test.

Post coital test – How is it performed?

There were several components to the post coital test.

• A woman would monitor for ovulation, typically with a home ovulation predictor test which measures the ovulation triggering hormone LH (luteinizing hormone).
• On the day after the ovulation kit turns positive (the actual day of ovulation), the woman and her partner would have intercourse.
• Shortly after completing intercourse, the woman would present to the fertility doctor’s office. The doctor would insert a speculum into the vagina so the cervix could be seen.
• With a small syringe, the fertility doctor would aspirate some of the mucus from inside the cervical canal and squirt in onto a microscope slide. The fertility doctor would, under high power magnification, count the number of moving sperm that were seen.

Post coital test – How do you interpret the results?

If no moving sperm were seen, the woman was said to have “hostile cervical mucus” and was declared infertile or unable to become pregnant though intercourse. Alternatively, if there were many moving sperm, she was said to be “normal. There were often one or two categories in between these extremes depending on the number of moving sperm seen.  

Post coital test – Why it was abandoned.

Studies going back to 1990 showed that the post coital test lacks validity to differentiate between fertile and infertile couple and reliability in terms of the consistency of its results. For example, the presence and number of swimming sperm in cervical mucus do not correlate with the probability of pregnancy. In 1998, a very well done in the Netherlands showed the test was not beneficial to couples. Couples were randomly assigned to one of two groups. One group underwent the post coital test (intervention group) and one group did not (control group). Couples were followed for two years. Those who underwent the test as a routine part of their infertility evaluation had more tests done overall and spent more money but showed no improvement in fertility.  

  This study gave fertility doctors level I evidence (a properly done randomized controlled trial) to support a class E recommendation (good evidence against the routine use of the post coital test). Stated another way, routine use of the post coital test is the exact opposite of evidence based medicine.