THE CERVICAL CYCLE
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 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.
Follicular Phase
The cervical glands proliferate under the influence of oestrogen 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.
Under the influence of estrogen, and as the time of ovulation approaches, 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.
Cervical Mucus at Ovulation
The 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.
Fern Test at Ovulation
The amount and character of the cervical mucous is an important diagnostic criteria for ovulation in cases of infertility.
Luteal Phase
During the luteal phase, 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.
During menstruation, cervical glands becomes 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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