Cervical mucus is naturally secreted by glands in the cervical canal, to fill and block the canal. This protects the uterus against unwanted intrusion by bacteria or other unwelcome small materials that may have found a way into the vagina. Of course, for conception to occur, the small materials called sperm must cross the threshold of the cervix and enter the uterus, in order to meet the released egg. Thus, at the time of ovulation, sperm must be welcome to pass through cervical canal1.

Like males, sperm are most comfortable in a somewhat basic environment, with a pH factor of around 7 or 8. Seminal fluid, unsurprisingly, has this pH level. Yet the vagina is a slightly acidic place, with a pH closer to 3, and not very hospitable to sperm once they stray from the seminal fluid. Sperm therefore need to get to the cervix and cross the mucus barrier with alacrity and get into the uterus if they are to fulfill their destiny.

Cervical mucus must allow sperm to pass, while remaining an effective barrier to other unwanted visitors. To facilitate this, the make-up of cervical mucus changes during the woman's monthly ovulation cycle2. In reaction to estrogen released at ovulation time, several changes occur in the cervical mucus:

  • The mucus becomes more alkaline, thus less deadly to crossing sperm;
  • The mucus thins and becomes more elastic, allowing the sperm to enter and travel;
  • The amount of mucus increases;
  • The mucus aligns into strands that create channels for the sperm to travel along.

When the mucus is in this state, sperm can typically live within it for 1 to 2 days, making their way into the uterus and up the Fallopian tubes in search of an egg. Couples trying to conceive may time sexual intercourse to get the sperm to the cervix at its most receptive, just prior to ovulation, thus maximizing the chance of fertilization3. After ovulation, the hormone progesterone causes the mucus to return to a thicker and more acidic state, the better to be a barrier to unwelcome organisms.

If the mucus does not make all of the pre-ovulation changes listed above, the sperm will be unable to pass through. Antisperm antibodies or white blood cells may also be attacking the sperm, damaging them before they complete their journey. This, then is 'hostile' mucus - mucus that does not support the passage of sperm during the critical ovulation period.


If couples have persistent and unexplained infertility, and the male partner's sperm quality is not suspect, then they may be tested for hostile mucus. There is no definitive test for cervical mucus. Most commonly, a sample of cervical mucus is taken just before ovulation. The sample may be taken 12 hours post-coital, or the male partner's sperm may be placed adjacent to the mucus sample. The results are then examined with a high-power microscope. If the sperm appear active and are making progress through the mucus, then all is well. If the sperm are active in the seminal fluid but are not moving into and through the mucus, then one or more hostile factors may be at work.


If the sperm are being attacked by white blood cells, this may be symptomatic of an infection in either partner, so treatment of that with antibiotics such as doxycycline would come first. That aside, if the mucus seems to be too thick, the female partner may try using Guaifenesin4 to thin the mucus. Other mucal problems are difficult to treat, and the fertility specialist may recommend Intrauterine insemination, which bypasses the mucus and places the sperm directly into the uterus.

An assisted reproductive technology node.

Created as a notional companion piece to poisonous sperm.


Please note that I am not a medical specialist. My expertise is that of personal experience. As always, nothing on Everything2 should be considered medical advice. Consult with your own medical doctor before making any decisions about your health. See also the Everything2 medical disclaimer.


  1. Biologically, that is, without regard for the opinion of the possessor of said cervix.
  2. During pregnancy cervical mucus thickens further to create a mucus plug which entirely seals off the uterus, to protect the growing fetus.
  3. Couples may use a fertility monitor to track hormone levels. If simply getting the sperm to the cervix naturally is a problem, an assisted reproductive technology procedure called cervical cap insemination may be used to place the sperm next to the cervix.
  4. Guaifenesin is the active ingredient in the cough syrup Robitussin.

Sources: Three long years of this shit.