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Part Three // How Hormonal Contraceptives Work

Perceptions of Birth Control: A collection of stories and themes that emerged from interviews with undergraduates using birth control at the University of Vermont

This series of blog posts is excerpts (edited so its not so academic) of writing from my undergrad research in 2021


Before I talk more about the findings, it is important to discuss the physiology of how the pill works as compared to cycling naturally. When someone is taking a pill everyday their hormones look a bit like the chart below  (these images are taken from Sarah E. Hill’s book).



When someone bleeds it is considered a withdrawal bleed because the synthetic hormones are not there anymore. Without the high levels of progestin the uterine lining sheds, this is what happens most of the time when one takes the sugar pills. When someone has a hormonal IUD they may still ovulate, but their uterine lining is thinned so much by the progestin that it becomes impossible (when working properly) to support implantation and thus pregnancy. This is why it is common to have some spotting/bleeding after getting a hormonal IUD inserted. 


In the case of the combination pill (that stops ovulation all together) physiologically the withdrawal bleed is not needed to confirm that a pregnancy is not happening (this is of course with perfect use). As Hendrickson-Jack writes, “There is no medical reason to induce a withdrawal bleed between pill packs. The number of days in a pill-induced cycle is arbitrary. [The manufacturers] could have easily selected 100, 36, or 75, but the 28-day pill cycle allowed women to think they were still getting their periods” (Hendrickson-Jack 97). If one were to miss some pills and ovulation were to happen that is when pregnancy could occur.



This second chart, also taken from the book This is Your Brain on Birth Control, shows the hormone profile of someone cycling  naturally. The first spike is what prompts ovulation and then the second spike is progesterone which has a naturally calming effect on the nervous system. Like the moon and ocean tides, there is a more of a long term ebb and flow when someone is cycling naturally.


Women are only fertile 6-7 days a cycle. Yes, every pententrative sexual encounter can not lead to a pregnancy. The question then must be asked: why does birth control control women’s bodies daily when it is really the sperm that are active every single day. But that is a conundrum for another project. 

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