Sympto-Thermal Method
The Couple to Couple League
Building Healthy Marriages through Natural Family Planning

Hormones affecting the female cycle

Ever heard that women are “walking, talking hormones?” While we prefer “beautifully and wonderfully made,” there is a shred of truth to the former phrase with regard to the hormones that drive the female fertilitycycle! Here is a brief synopsis of how four hormones affect the female cycle.

Phase I begins with a woman’s menstruation or period, which is triggered by a drop in the hormone known as progesterone, as the corpus luteum (the empty egg sac left in the ovary after ovulation) from the previous cycle ceases to function. Phase I is an infertile time of the cycle; no ovarian activity is occurring.

Phase II, the fertile time, begins when another hormone, follicle stimulating hormone (FSH), is released from the pituitary gland. FSH causes some immature eggs to develop in the ovary. These follicles produce the hormone estrogen, which in turn causes two of the three signs of fertility used in CCL’s sympto-thermal method: the production of cervical mucus and the opening and softening of the cervix. Estrogen also causes a build-up of the lining in the uterus, and the release of another pituitary hormone known as Luteinizing Hormone (LH).

LH causes the follicle to ovulate and release the mature egg. Now empty, this follicle becomes the corpus luteum and releases progesterone. Phase III begins sometime after the release of progesterone and is an infertile time of a woman’s cycle. Phase III, the return to infertility, results in the cervical mucus drying up, the cervix closing and hardening, and most notably by the third sign of fertility — a rise in temperature.

This graph depicts the levels of estrogen and progesterone at various times during the cycle. Notice that estrogen (green line) builds up during the first half of the cycle, and then drops off somewhat after the release of the progesterone following ovulation. It is easy to see that estrogen is the more dominant hormone of the two before ovulation; whereas, progesterone (blue line) is more dominant after ovulation. It is important to note that, although one hormone is dominant in each half of the cycle, both hormones are still present throughout the cycle. A woman’s body continually produces some of each of the hormones, but in differing amounts at different times. In fact, in the second half of the cycle there is still a relatively significant amount of estrogen being produced; but in comparison, progesterone production surpasses it, and hence, is the dominant hormone at that time.

This graph shows the levels of the pituitary hormones, FSH and LH, during the cycle. Both of these hormones are at their highest levels during the early and middle parts of the cycle, with FSH (red line) at a higher level than LH very early in the cycle. Both reach their peak amounts about mid-cycle in a typical 28-day menstrual cycle. In shorter or longer cycles, the peak amounts of FSH and LH would occur approximately two weeks before the onset of the next period. As ovulation approaches and the levels of estrogen increase, the influence of estrogen produced by the ovary signals the brain to release higher doses of LH (orange line). It is the surge of LH around mid-cycle that triggers the release of the egg from the follicle in the ovary, or ovulation. After this point, both FSH and LH play a less prominent role.

This description of how four key hormones relate to a woman’s anatomy and to the phases of her menstrual cycle points out the scientific principles that form the basis for NFP. Natural Family Planning is based on observable scientific facts. As mentioned, these four hormones are responsible for the changes that occur in the female cycle, and they also produce observable signs that most women can detect. By recognizing these observable signs — cervical mucus, the basal body temperature and the cervix — every woman who has a healthy menstrual cycle can usually identify when she is fertile and infertile.

For more on how signs of fertility are used in CCL’s NFP method, go to Sympto-Thermal Method of NFP.

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