Written by Dr.M.D.Mazumdar, MD
Where is the cervix?
And why does the cervical mucus change at the time of ovulation?
The cervix can be felt in the apex of the vagina. When a woman squats down and pushes her fingers gently into her vagina, she will feel a firm rounded structure in the upper part of the vagina - that is the cervix.
If felt carefully, a small opening in the middle of the cervix will be noticed. This is the external os and is the opening through which the uterus communicates with the vagina and through which blood and other discharges come out during the period.
In women who have never had chldren, the external os is very small, almost pinpoint and rounded. After the postpartum period, the external os is more slit-like than rounded. This is because, during childbirth, the cervix dilates up to 10 cm to accomodate the head of the baby and it never goes nback to its former shape.
The changes that occur in the cervix in response to oestrogen and progesterone secreted by the ovaries, is termed the Cervical Cycle of menstruation.
The changes in the cervical cycle is mainly recognised by the changes that occur in the cervical mucus. These changes in the cervical mucus is important because it can help in the diagnosis of ovulation - especially important in women who are planning a pregnancy or undergoing treatment for infertility.
The cervix, like the uterus, has three phases in the menstrual cycle, although, unlike those in the uterus, the changes are not very distinct.
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The cervical glands proliferate under the influence of estrogen secreted during the follicular stage of the ovarian cycle . The glands become longer as the follicular cycle progresses. The glandular epithelial cells become larger and start to secrete a mucus that is initially thick and viscous. At this time, the cervix feels firm and higher in the vagina.
As the time of ovulation approaches, the level of estrogen increases and the quality of the cervical mucus begins to change. From about the 10th day of the cycle till ovulation on the 14th - 16th day, the mucus becomes profuse, more watery and tenacious. It begins to resemble egg-white - clear, profuse, and slippery. The consistency of the cervix also changes, becoming softer, smoother and it can be felt somewhat lower in the vagina.
The cervical mucus becomes so tenacious that it can be stretched in threads up to 10-15cm long at the time of ovulation. This quality of the mucus is called 'spinnbarkeit' and is used for the thread test to diagnose ovulation.
The amount of cervical mucus may be so profuse as to be termed the 'vaginal cascade'. This watery cervical mucous helps the sperm to swim into the uterus to fertilize the ovum.
During this time, if the cervical mucus is collected on a clean glass slide and is allowed to dry, it will form a characteristic pattern that resembles the fronds of a fern. This can be observed under a microscope and is known as 'ferning' or the 'fern test'. It is another important diagnostic criteria of ovulation. Ferning can be seen from the 6th to the 22nd day of the cycle,becoming most prominent at around the 12th-16th days.
The amount and character of the cervical mucous is an important diagnostic criteria for ovulation in cases of infertility.
During the luteal phase, the level of estrogen gradually decreases and the progesterone level begins to rise in the blood. Under the influence of progesterone, the cervical mucous changes its physical properties. It becomes thick and viscous and forms a more secure cervical plug. It resists penetration by sperm. The water content of the mucus becomes much less and it also loses its ability to stretch without breaking.
These changes in the cervical mucus are related to an increase in protein content, reduction in electrolyte content and the presence of phospholipids. Both the properties of spinnbarkeit and ferning is lost.
The cervix also becomes firmer. It once again feels similar to the consistency in the early part of the follicular phase.
During menstruation, the cervical glands become smaller and narrower and becomes slightly desquamated.
After menopause, the cervical secretions becomes lesser and lesser in association with the decreasing levels of estrogen.
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