Health: What you don't know about your menstrual cycle

It is important for all women to know what is going on in their bodies during their menstrual cycle. That is why I have written this piece which was a note I took while listening to a lecture on menstrual cycle.


The menstrual cycle is generally between 24 – 35 days. A lot of women’s cycle is 28 days but it tends to vary in different women: very few women have periods that last for 24 days and very few women go beyond the 35 days range.

The menstrual cycle as a whole starts from the actual menses this is the slophing off of the endometrial lining and the actual bleeding. The hypothalamus (within the brain) signals the release of Gonadotropin Releasing Hormone (GnRH). This hormone is released every 60 – 90 minutes and it triggers the release of two hormones which are the Follicle Stimulating Hormone (FSH) and the Luteinizing Hormone (LH). These two hormones are resident right below the hypothalamus.

When these two hormones are released, they trigger the release of Estrogen and Progesterone in the Ovary. The estrogen is responsible for thickening of the endometrial lining. Progesterone works in post ovulation to prepare the endometrial lining for implantation. In the Cervix, the Progesterone works works to thicken the mucus which would act as a plug to prevent sperm from entering the vagina. The Estrogen and Progesterone have a feedback system that affect the level of FSH and LH hormones as well as the GnRH.


The different phases of the menstrual cycle are the

Follicular Phase: The first phase is the follicular phase. This is where a viable follicle is developed for ovulation. The main hormones that work here are the FSH and LH. During the first five days of the follicular phase, 20 – 50 follicles are stimulated and in the first 5 – 7 days, one of these follicles become dominant and continues development. The length of this phase varies: it can run from 10 -18 days. This variation is the cause of variation in the length of cycle for different women.

The Ovulatory Phase: This is when the dominant follicle is released (that is, the release of a fertilisable ovule) in conjunction with higher levels of estrogen which causes a surge in the LH which signals that ovulation is happening. The ovulation prediction kits in grocery stores are actually measuring the surge of the LH which is a very reliable indication that ovulation is about to happen.

The Luteal Phase: This phase is a constant 14 days, there is no variation at all in the number of days in this phase. Progesterone level dominates in the phase. The rise of progesterone means that ovulation has already occurred: it does not predict ovulation. This rise in progesterone also coincides with the rise in the basal body temperature of a woman.

At the time of ovulation, many things are happening which includes the LH surge and the rise in basal body temperature. If fertilization and implantation does not happen, corpus lutem is developed and goes through atresia as the level of hormones drop. The levels of these hormones drop because fertilization has not happened. A shedding off of the endometrial lining (menses) then occurs which lasts for about 4 – 6 days to then signal the end of the menstrual cycle. The level of hormones in the Luteal phase starts to signal the readying of the next cycle.