Every woman has probably experienced at some point the decreased patience or craving for chocolate that can occur once a month. It is well known that women have a monthly cycle in which there are hormonal variations, but do you know what is happening throughout the month that can cause mood changes and other symptoms? Here is a brief overview:
The average female cycle is 28 days long and is spilt into two main phases: the follicular phase, lasting from the onset of menses to ovulation, and the luteal phase, lasting from ovulation to the onset of menses. The luteal phase is fixed at fourteen days long, and the follicular phase averages about 14 days but can be more variable. This variability can occur because the follicular phase is dependent on estradiol reaching levels that can trigger the release of luteinizing hormone (LH). The time it takes estrogen to reach the right amount can vary depending on each individual.
As explained in the previous post, sex hormones are controlled via mechanisms in the brain. Follicle stimulating hormone (FSH) and LH are released from the pituitary, following a signal from the hypothalamus, and follow specific trends throughout the cycle. FSH peaks first on about day 3 of the cycle and is responsible for recruiting a follicle. As the recruited follicle matures, estradiol builds gradually until it peaks around day 13. During this time, estradiol facilitates the growth of the endometrial lining. The peak in estradiol stimulates an LH surge 12-24 hours after the estradiol peak, which induces ovulation. After ovulation, the follicle forms the corpus luteum and progesterone levels begin to rise. Progesterone peaks on day 21 of a regular cycle, or 7 days before the menses. If ovulation doesn’t take place progesterone will not increase and a peak will not be seen on day 21. The cycle begins again when the drop in progesterone and estradiol cause the shedding of the endometrial lining, or menses.
As the female cycle is characterized by hormone patterns, dysregulated patterns can result in a variety of clinical symptoms which we will detail in a coming blog post. More information on the hormone patterns associated with the female cycle can be found in Module 3 of the Reproductive Endocrine Curriculum found here (log in required).