Frequent bowel movements are a potential source of a reduced quality of life in patients. It can be bothersome to always worry about a sudden urge to rush to the bathroom. When it comes to a woman's menstrual cycle, this can also lead to a reduced quality of life with a similar dependence on being close to a bathroom during the crest of the cycle. Do these two separate events share some type of overlap or are they truly independent? Here, we will determine if there is a link between a menstrual cycle and frequent bowel movements.
Does the Menstrual Cycle Lead to More Bowel Movements?
It seems that these two events share a lot of common characteristics. Both are marked by increased pressure on the pelvis and can lead to increased rectal tone. As we saw when we explored the link between coffee and bowel movements, when there is an increase in internal rectal pressure, there will be a stimulus to find the nearest toilet and relief the pressure .
According to research, there is already an established connection between an exacerbation of irritable bowel syndrome and a menstrual period. The reason behind this is that even healthy women naturally have looser stools at the time of their menses .
A mechanism that can attempt to explain why this happens is during the menstrual cycle, the tissue lining the uterine wall falls off and is removed thanks to contractions from the uterus. As the uterus contracted, it can inadvertently also alter the tone of the rectal sphincter. This increase in intra-abdominal pressure is similar to the same force you generate yourself when you are attempting to defecate normally. This phenomenon is the point when you "push" out the fecal matter.
During a period, women also typically complain of symptoms like heaviness and bloating so it is no surprise that this may lead to more frequent bowel movements.
Why Do Bowel Movements Happen More Often During Menses?
Even if the increased pressure may also help explain why there is an increase in bowel activity during your period cycle, the real culprit for why this happens is due to the hormone changes that occur during menses. During a typical 28-day cycle for women, there are three distinct phases marked by changes in the hormone levels in the body. At the beginning of a period cycle, there are moderate levels of both estrogen and progesterone that help grow the tissue lining the uterus to prepare the uterine cavity for potential pregnancies. Levels of both hormones continue to increase until the half-way point of the menstrual cycle, around day 14. This is the period called ovulation where the egg is released into the uterine cavity and progesterone levels are the highest in case of potential egg fertilization.
If the egg that the woman had released is not fertilized by a sperm after a day or two, progesterone and estrogen levels begin to dramatically drop and the tissue in the uterine cavity begins to thin. At the end of the menstrual period, progesterone levels are at the lowest point of all during the entire cycle.
Not only is progesterone responsible for maintaining the integrity of the uterine tissues, it is also a natural way to regulate your bowel activities. Progesterone naturally reduces your desire to defecate slightly but when values fall, this inhibitory effect is lost so women can experience bouts of diarrhea during the menses stage. Stools are generally the loosest during the first 48 hours of a new cycle but as progesterone levels begin to climb once again, diarrhea episodes stop and women regain control of their bowel function. 
An interesting caveat to our exploration of a menstrual cycle and frequent bowel movements is the status of the female at baseline. In one cohort study on a Japanese population, it was seen that women who had normal bowel habits after menses tended to have a less obvious increase in frequent bowel movements. If, however, the women tended to be more constipated during their cycle, there was a more significant increase in the number of bowel movements that would be experienced during menses. 
Again, the deciding factor in who will experience this constipation would be women who have higher levels of progesterone. As a broad generalization, this would typically be younger women who have not yet had children compared to an older mother still on her periods. As a woman ages, the intensity of diarrhea should subside slightly as you move towards menopause when estrogen and progesterone should lower and finally stabilize.