“Oh yeah, that was a lie,” said my AP Chemistry teacher when a student asked about the tiny-orbiting-balls model of the atom we’d learned in basic chemistry the year before. We were a year older now, and on to the VSEPR model of the atom, in which electron orbits weren’t tiny whizzing planets but instead were probability gradients, expressing the likelihood of observing an electron in a given spot. What we had learned the previous year had been good enough as a general approximation, but it was a long way from true, and we’d reached the point where the oversimplifications of the earlier model could get us into trouble.

I didn’t realize that my high school sex-ed class had been taught the same way—minus the eventual confession of inadequacy—until I got engaged and started reading about Natural Family Planning.

In middle- and high-school sex ed, my class was taught that puberty marked the beginning of a lot of strange changes to our bodies. We got to see a cutaway torso illustrating where the ovaries were, and where that blood would be coming from, and we got explanations of several different methods of tidying up during the several days per month when our reproductive systems would be relevant to us.

But when I picked up Toni Weschler’s Taking Charge of Your Fertility, a handbook on fertility tracking (intended for a wide audience, so it discusses some options that aren’t relevant to Catholics like me), I felt as I had in that AP Chemistry class, suddenly finding out what a weak approximation of my body I’d been taught to accept as authoritative.

One of Weschler’s repeated complaints is that women are taught that the median women’s cycle (28 days, ovulation on the 14th day) is the normal woman’s cycle. This is the fundamental mistake of the rhythm method of avoiding pregnancy, which suggests just using a calendar to track fertility, rather than the combination of basal body temperature, cervical fluid, and several other indicators used by NFP methods. It’s a mistake Weschler’s clients’ doctors have made, using the medians to estimate the gestational age of their patients’ babies, ignoring women’s explanations that they’ve never had a cycle as short as 28 days, that they didn’t even have sex in the window in which the doctor thinks conception happened, and that therefore the baby probably isn’t really small for its age.

I was intending to read the book as an instruction manual, but I kept recognizing myself in the stories of the women who she worked with. At least twice, I dog-eared a page not because it would be relevant to charting for my married life, but because Weschler was explaining that something about my body was normal—maybe not the median experience, but well within the range of normal. I’d gotten used to the idea that there were always a couple things wrong with my body, in this domain and others, because all the discussion I’d heard was about either ideals or averages. Learning NFP has meant reacquainting myself with my body and its own, particular dignity.

But maybe I shouldn’t have been so surprised. Whenever I read books about women, written for women, I tend to have this experience, whether it’s Weschler’s explanation of NFP and why women can’t be rounded down to the median menstrual cycle or Emily Nagoski’s book on female sexuality, which explains that women don’t need to feel deficient when they don’t match the model of spontaneous (as distinct from responsive) sexual desire. The problem isn’t the way most women are built, but rather the fact that we’ve been told to accept the median male experience of sexual desire as the normative ideal for everyone—women included.

Reading about NFP helped me learn that some features of my body and my cycle weren’t problems at all, and it gives me tools for spotting real problems if they come up. When my future husband and I are married, if we have problems with infertility, NFP charting will give us clues about what might be going wrong. Are we missing my fertile times? Is the second stage of my cycle too short for a fertilized egg to implant in the uterus? It’s been a relief to see some of those problems ruled out ahead of time, as I practice charting, and to know, if we run into difficulties, that we’ll be better prepared to figure out what treatments (if any) could help.

Finally, it’s been nice to change my understanding of my cycle from a semi-random occurrence, only relevant during the moments I was actually menstruating, to a whole, cohesive system. Nerd that I am, I’ve even liked being able to wake up in the morning, observe a temperature drop, and know I’ll start my period that day—it all makes a lot more sense than knowing that cramps mean my period will start in 1-3 days.

Being engaged means I have to learn all this now, but I wish I’d learned the basics of NFP in my high school sex ed classes, and I’ll teach it to any daughters I have long before they’re going on dates. I like being able to approach my body with more of the “Huh, that’s neat” wonder that my science classes sparked—not the “Here’s how you manage a problem” attitude of my sex-ed classes.

This week is NFP Awareness Week, and I recommend Weschler’s Taking Charge of Your Fertility for a beginner-friendly explanation of fertility charting. Simcha Fisher’s The Sinner’s Guide to NFP covers the “How?” questions that go beyond the logistics of charting—How do I balance prudence and generosity? How do I express and receive love during periods of abstinence? and so on.

Leah Libresco is a blogger for Patheos and works as a statistician in New York City. Her first, recently published book is called Arriving at Amen: Seven Catholic Prayers That Even I Can Offer.

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