The changes in the mucus reflect a highly complex chain of events in the body’s hormonal system.
As the cycle begins, the pituitary gland at the base of the brain starts to produce two chemical messengers, Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). The over-riding control of FSH and LH production occurs in the area of the brain called the hypothalamus which acts like a computer – analyzing nerve signals from other areas of the brain, including those generated by emotions and environmental factors, as well as assessing hormone signals relevant to fertility.
The follicles (that is, the groups of immature eggs within the ovaries) have a threshold requirement for FSH below which no stimulation occurs (that is, the FSH has to reach a certain level in the bloodstream before the follicles will start developing). During the early infertile days of the cycle the FSH level is below the threshold, and any discharge is commonly sparse and dense or absent altogether. These days, when the pattern is unchanging, are recognised as the Basic Infertile Pattern (BIP).
Once the FSH level passes the threshold, a group of follicles begins to develop. The follicles produce the hormone, oestrogen. At this point, if you have experienced dry days, you will notice mucus; if your BIP was one of an unchanging discharge, you will now notice that there is a change in the sensation produced at the vulva and/or in the appearance of the discharge.
When a follicle is developing satisfactorily, it produces the hormone oestradiol, an oestrogen, which acts as a signal informing the brain of the level of ovarian activity. In response to a high oestradiol level, the pituitary gland slows down its production of FSH and releases a series of surges of LH over a period of forty-eight hours. The dominant follicle rapidly matures and important changes take place in the chromosomes of the ovum (egg cell) – which contain the inherited genetic material.
The peak LH level triggers ovulation about seventeen hours later. The LH is also responsible for the production of the corpus luteum which forms from the empty follicle in the ovary after the release of the ovum.
After ovulation, the corpus luteum produces the hormones progesterone and oestradiol. These are necessary for the continued growth and development of the nutritive endometrium in preparation for possible implantation should a sperm cell fertilise the ovum.
In the absence of pregnancy, the production of these hormones begins to decline after about 6-7 days, removing the hormonal support for the endometrium, which is shed when menstrual bleeding commences 11-16 days after ovulation, and so a new cycle begins with a rise of FSH.