No doubt about it, menstrual periods tend to get a bad rap. Between the mess, the inconvenience, and the expense of menstrual products, it’s no wonder so many women wonder if they really need to have a period each month. In fact, CNBC News recently reported on the formation of The Tampon Tax Back Coalition, which promises to compensate consumers for the state sales tax many pay on their tampons and other period care products. Frustratingly, the sales tax is added to all “nonessential” items, whereas “essential” items like food and medicines are tax-exempt. Here at Natural Womanhood, we’ve always known that regular periods are essential for women’s health. In our Reasons Women Need Periods (RWNP) series, we’ve explored how the menstrual cycle helps the female body in a host of ways, from brain health to bone health to immune health. In this latest installment of RWNP, we explain how the menstrual cycle quite literally prepares the body for a healthy future pregnancy.
Pregnancy is an inflammatory event…
After an embryo implants in the lining of a woman’s uterus, a biological chain reaction takes place. Her uterine arteries become highly dilated blood vessels to supply blood to the trophoblast, which is the outer layer of the blastocyst (one of the very earliest stages of human development). The placenta develops from the trophoblast, and the rapidly growing embryo derives his or her oxygen, hydration, nutrition, and waste management from the placenta via the umbilical cord.
If all of that sounds a bit… invasive, that’s because it is! In fact, as a 2009 article from the American Journal of Obstetrics and Gynecology notes, human beings are one of a few species where “placenta formation entails deep trophoblast invasion of maternal tissues and its vasculature” [1]. This deep infiltration of the mother’s tissues by a genetically distinct entity (i.e., the baby and the placenta) means that during implantation and pregnancy, the mom’s uterine cells undergo some temporary damage due to inflammation. As it happens, menstruation is also an inflammatory event [2].
… and menstruation is, too
Because of the deep infiltration of maternal tissues required for proper implantation of an embryo, endometrial decidualization, or the changes that happen in the endometrium to allow the growing embryo to implant, plays a major role in future pregnancy health. Notably, endometrial decidualization occurs during the second half of each menstrual cycle, even if pregnancy doesn’t occur.
A major way we might encourage a future healthy pregnancy, then, is to regularly allow a woman’s body to undergo the process of endometrial decidualization, and then shed its lining during her period. Menstruation helps protect the cells of the uterus from hyperinflammation (too much inflammation) and oxidative stress associated with pregnancy [1]. This is because the uterus gets a sort of “practice run” with menstruation.
In a 2020 article from the International Journal of Molecular Scientists, the authors thus conclude that “the primary driver of pregnancy health is the quality of the soil, not the seed” [3]. (In this metaphor, the soil is the endometrium, and the seed is the embryo.) Far from an “evolutionary coincidence,” then, menstruation appears to be crucial for what one might call “cultivating the soil” for the health of future pregnancies [1].
Healthy, regular inflammation via menstruation may be protective against preeclampsia
Notably, in a case-control study of infertile women who became pregnant after receiving treatment, those with a history of endometriosis-related infertility were less likely to develop preeclampsia [4]. This was the opposite of what the researchers expected. Could prior inflammatory events in a woman’s body precondition her to handle pregnancy-related inflammation without progressing to preeclampsia? The authors of the aforementioned American Journal of Obstetrics and Gynecology article note that endometriosis might be a malfunctioning of the body’s normal inclination to precondition the body for pregnancy [1]).
Interestingly, previous research correlated preeclampsia with a lack of regular menstruation [5]. In a 2023 article for FACTS about Fertility, medical student Kathy Fatovic developed a theory behind why that might be the case.
As Fatovic wrote, preeclampsia is more severe in younger women (under twenty years old) than it is in older women. One possible explanation might be that younger women have, on average, obviously not experienced as many regular menstrual cycles as older women have. Thus, younger women’s bodies have not been as preconditioned to handle inflammatory events as the bodies of older women have.
Is preeclampsia an autoimmune problem?
Fatovic notes that the exact causes of preeclampsia are unknown, though increasingly researchers suspect an autoimmune component. Abnormal development of the placenta (which, like the embryo, is genetically distinct from the mother and deeply infiltrates the maternal tissues and vasculature) almost certainly plays a role. Consequently, low-level inflammation via repeated, regular menstruation may help prepare a woman’s body to react to pregnancy-associated inflammation.
Certainly, more research is needed, especially given that endometriosis generally decreases a woman’s chances of conceiving. Perhaps in the subset of women with endo who do go on to conceive, prior inflammation serves to decrease the body’s response to pregnancy-related inflammation.
Preeclampsia is not the only pregnancy-related condition that may be at least partially prevented by regular menstruation. Miscarriage, gestational diabetes, and preterm birth, may all be related to problems with implantation and placenta formation. In fact, as those same authors note, “Humans are one of only a few mammalian viviparous species in which decidualization starts during the latter half of each menstrual cycle” [3]. The uterus, then, needs to be prepared well before pregnancy to maximize the chances of successful implantation and a healthy pregnancy.
Hormonal birth control deprives women of the menstrual cycles that prepare them for healthy pregnancy
We can see how important it is that women have a regular, healthy menstrual cycle to prep their bodies for future successful pregnancies. But this preconditioning does not occur when women are taking hormonal birth control, because it stops women from cycling all together. Again, we’re reminded that there are many reasons why women actually do need their periods! More research is needed to understand the full benefits of routine menstruation, but what has been discovered so far is encouraging for those who want to protect and monitor their fertility (and/or plan their families) via a Fertility Awareness Method–even if pregnancy is a long way off.
References:
[1] Brosens, Jan J et al. “A role for menstruation in preconditioning the uterus for successful pregnancy.” American journal of obstetrics and gynecology vol. 200,6 (2009): 615.e1-6. doi:10.1016/j.ajog.2008.11.037 [2] Evans J, Salamonsen LA. Inflammation, leukocytes and menstruation. Rev Endocr Metab Disord. 2012 Dec;13(4):277-88. doi: 10.1007/s11154-012-9223-7. PMID: 22865231. [3] Ng SW, Norwitz GA, Pavlicev M, Tilburgs T, Simón C, Norwitz ER. Endometrial Decidualization: The Primary Driver of Pregnancy Health. Int J Mol Sci. 2020 Jun 8;21(11):4092. doi: 10.3390/ijms21114092. PMID: 32521725; PMCID: PMC7312091. [4] Brosens, Ivo A et al. “Endometriosis is associated with a decreased risk of pre-eclampsia.” Human reproduction (Oxford, England) vol. 22,6 (2007): 1725-9. doi:10.1093/humrep/dem072 [5] Bonnesen, Barbara et al. “Women with minor menstrual irregularities have increased risk of preeclampsia and low birthweight in spontaneous pregnancies.” Acta obstetricia et gynecologica Scandinavica vol. 95,1 (2016): 88-92. doi:10.1111/aogs.12792Additional Reading:
FAM Basics: Everything you need to know about your endometrium
Preeclampsia: What causes it, who develops it, and how do you prevent it?
