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Cervical mucus is a jelly-like substance produced by tiny glands in the cervix called cervical crypts. It has a protective function and may prevent bacteria from getting into the uterine cavity. The mucus changes predictably and cyclically during the menstrual cycle. During the first half of the cycle before ovulation, when the hormone estrogen is produced in ever-increasing amounts, the mucus made by the cervical glands becomes watery and copious. Sperm can penetrate the watery mucus easily, and when intercourse takes place, they swim through it into the uterus.
After ovulation, the quality of the mucus changes because the corpus luteum of the ovary now starts to make the hormone progesterone. Mucus produced under the influence of progesterone is thicker, stickier and its quantity is reduced. Sperm cannot swim through this mucus, and it forms a barrier to sperm entry into the uterine cavity.
Even if intercourse occurs at the time the cervical mucus is at its most favorable, only about 1 in every 2000 sperm enter the mucus. The rest of the sperm remain in the vagina, where they die, because of the acidic pH of the vagina. Those sperm that have entered the mucus can survive there for long periods - certainly for several days after intercourse. Once in the cervical mucus, they steadily swim upwards from it into the uterus over a period of 48 to 72 hours. Thus the cervical mucus acts as a sperm reservoir, to be banked on if intercourse does not take place at ovulation. This is why you don't need to have sex every day in order to conceive! The cervical mucus also acts as a filter - and allows only the best sperm to swim through it into the uterus and up towards the egg present in the fallopian tube.
Mucus flows from the cervix down the walls of the vagina and can be observed when it reaches the vulva. You can learn to observe the changes in your mucus by becoming aware of the wet, lubricative feeling produced by the mucus, and by observing the mucus itself at the vulva. This is called the Billing (fertility awareness) method and is very useful in allowing you to determine when you ovulate.
You need to chart what the mucus looks like and feels like daily, from the day your bleeding stops. You will find the mucus present at your vaginal opening - the vulva. Remember, you do not need to feel inside the vagina; this will simply confuse the picture because the vagina is always moist. It is the vulva which is the mucus (fertility), monitor.
In a typical 28 days menstrual cycle, at the end of bleeding, the sensation you experience is one of dryness and no mucus is seen or felt. In some women, there is some mucus, but it is thick, sticky, and scanty. This is the basic infertile pattern of dryness and lasts for two to three days. Once this is over, you may notice a feeling of moistness at the vulva and the mucus will change in appearance and feel. It becomes thinner, clearer, more profuse, and stretchy, like raw egg white. This fertile-type mucus produces a slippery wet lubricative sensation at the vulva. The last day of this fertile-type mucus That is, the vulva feels lubricative) is called the peak of fertility, because it is the most fertile day of the cycle. You will know it is the last day only in retrospect; and after this, the important to realize that the peak day is not necessarily the day of the highest mucus formation; it is simply the last day that the mucus discharged has fertile characteristics. Ovulation usually occurs with 24 hours of the peak mucus signal. Therefore, these are the best days to have intercourse in order to maximize the chances of conception.
Fig 1. Normal cervix
Fig 2. Profuse cervical mucus
Fig 3. The Billing calendar for charting cervical mucus. The time period marked C is the "fertile period".
In some women, the cervical mucus may prevent the sperm from moving freely into the uterus. Such a barrier maybe because of the following reasons:
Problems with cervical mucus usually cause no symptoms. Tests need to be done to assess whether the mucus is normal or not.
The doctor examines the cervix and the cervical mucus daily from about the tenth day of the period. The mouth of the cervix is graded, depending upon how open it is; and the mucus is graded for its amount; its stretchability ("spinnbarkeit"); and its ability to fern. For the ferning test, a small drop of mucus is placed on a glass slide and allowed to dry. It should crystallize, forming branches which look very like fern leaves. These grades are added to give an Insler mucus score. Healthy cervical mucus is profuse in volume; very stretchable (up to 10 cm in length); and ferns easily.
The post-coital test (PCT):- This is one of the oldest tests in investigating infertility and has been done for well over 100years. Timing the PCT is critical, and it must be done in the preovulatory period when the mucus is profuse and clear. The gynecologist examines a small sample of the cervical mucus under a microscope some hours after sexual intercourse. The mucus is sucked painlessly from the cervical canal during an internal examination. Most doctors feel that the best time to do this is about 6 to 24 hours after sex, but this timing is not critical. The test is said to be positive if much normal live sperm are seen swimming in the mucus sample. The sperm should be swimming in a fairly straight line and reasonably vigorously. A positive PCT is very reassuring and implies that :
What if the PCT is negative (that is, no sperm are seen in the mucus, or they are all dead)? Some of the reasons for a negative test are:
Remember that a negative test is meaningful only if it is repeatedly negative under perfect conditions.
We never do the PCT test in our practice, because we feel it provides very limited information and does not affect the treatment plan.
If the mucus is good but the post-coital test is repeatedly bad, an 'in-vitro' mucus penetration test, or sperm invasion test, can be performed. This is performed simply by putting a drop of freshly removed mucus next to a drop of freshly ejaculated semen on a microscope slide. The interface between the two drops is examined for about a quarter of an hour, and it is then possible to see if the sperm are penetrating the mucus and swimming actively in it. If this does not occur, then it is likely that there is some form of immune response between the sperm and the mucus, and further tests should be conducted to examine this.
Cross-over testing can be performed using the mucus and semen under examination in various combinations with donor mucus and semen. This will show if the problem is with the sperm or the mucus.
Another simple test for anti-sperm antibodies in the mucus is called the sperm cervical mucus contact test (SCMC for short) where the sperm and mucus are mixed together. If under the microscope, the sperm are seen to be shaking in a characteristic way, this means that there are anti-bodies present.
Cervical problems can be corrected depending upon what the cause is. For example, if the reason for the poor mucus is:
For resistant cervical problems, the easiest solution may be to bypass the cervix entirely, by injecting the sperm directly into the uterus - intrauterine insemination.
Sometimes the problem is one of "cervical hostility " to the sperm - that is there are anti-sperm antibodies in the mucus that are killing the sperm. For this condition the outlook is now more hopeful: