Effectiveness of the Sympto-thermal Method of Fertility Awareness

This excerpt from The Cycle was written by Jennifer Aldoretta

I know what you’re thinking: “I totally love that this super awesome method is natural…but is it effective?” How well a method works is often one of the first questions we ask about birth control, and for good reason! So why didn’t I get into all this right at the beginning? We tend to be especially skeptical of natural birth control—especially since the most commonly discussed natural method is the rhythm method, which has a high failure rate—so explaining why the sympto-thermal method of fertility awareness (STM) is so effective is an important part of the conversation. Now that we got the why out of the way, we can finally get started on the how.

The sympto-thermal method of fertility awareness approaches the pill and other hormonal methods in its ability to prevent pregnancy [33] and is reported to be 99.6% effective with perfect use according to Planned Parenthood [34]. However, Planned Parenthood’s website doesn’t list the specific rules that must be adhered to in order to achieve this low, 0.4% failure rate. If the “Dry Day Rule” is adhered to, an effectiveness of 98% is achieved with perfect use [35], whereas adherence to the “Doering Rule” in addition to the “Dry Day Rule” results in an effectiveness of 99.6% with perfect use [36]. There are studies out there that list pregnancy rates greater than 20%, but I’d like to do a little myth busting and talk a bit about why this statistic is incredibly misleading.

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There are several reasons that high failure rate stats of 20% or greater should be taken with a grain of salt. Disparities among statistics often stem from studies grouping many “Fertility Awareness-Based Methods” into a single category. These “FABMs,” as they are called, often include the rhythm method, the standard days method, the two-day method, and the sympto-thermal method. While these methods are all considered “natural,” STM is by far the most effective because it accurately (and scientifically) detects both the beginning and end of the fertile window for each individual cycle. In my opinion, grouping these methods into a single category when discussing effectiveness would be like grouping male condoms, female condoms, sponges, diaphragms, spermicide, and cervical caps into one category and saying that “barrier methods” are only 70% effective. This wouldn’t make much sense, especially since we know that male condoms are much more effective than the others. So you can see why lumping these “FABMs” together is misleading.

Another cause for confusion is “typical” versus “perfect” use failure rates. Oftentimes, information regarding the sympto-thermal method will report “typical” use failure rates. I’m not saying that this in itself is misleading, but since hormonal contraceptive methods routinely advertise their “perfect” use failure rates, viewing the two stats side-by-side gives people the wrong perception about both methods. We all know that when used correctly 100% of the time, hormonal contraceptives have failure rates of less than 1%. But what many of us don’t know is that the typical (or average) use failure rate of oral contraceptives—missing pills every now and then, taking pills at different times each day, etc.—is closer to 9% [37]. I’m sure it can be even higher for groups that adhere particularly poorly to the pill regimen. A 2011 survey of 1200 women—with 305 respondents—that was published in the Journal of Women’s Health reported that 11% experienced an unplanned pregnancy while using oral contraceptives [38]. My point, folks, is that there’s a lot of misleading information out there, and we really need comprehensive information about a birth control method before deciding to use it.

Like the pill, STM failure rates increase if you don’t use the method properly. My argument for STM is that knowing when a you’re fertile and very likely to get pregnant makes the decision not to have unprotected sex pretty easy if you’re serious about not wanting babies! On the other hand, if you accidentally miss a few pills, you cannot quantify the additional risk you will encounter. When using STM, taking chances in the fertile phase by having unprotected sex quickly excludes you as an “STM user” and propels you into the category of “no contraceptive use”. Blatant disregard for the rules is really synonymous with not using a method at all. Similarly, it doesn’t make much sense to include couples that have unprotected sex in the failure rate calculation for condoms. Nor does it make much sense to include someone who simply chooses to stop taking the pill in the failure rate calculation for oral contraceptives.

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The big takeaway from this whole spiel is that proper use of STM—meaning no unprotected sex in the fertile phase—is highly effective at preventing pregnancy. And while the method will be most effective as a way to prevent pregnancy if you abstain during the fertile phase, studies have shown that a barrier backup can also be used with little to no impact on overall efficacy [39]. This is particularly useful for couples that don’t like the idea of limiting their options. Be aware, though, that pregnancy risk in this case will depend on the failure rate of whatever back-up method is used during the fertile phase.

Keep in mind that anyone has the ability to use a method of birth control perfectly when educated properly on its use. A comprehensive understanding of STM and female reproductive biology will only increase a couple’s confidence in their use of STM or whatever other method of contraception they decide is right for them.

A Little Something Extra

If you find yourself pining for more STM information after reading this part of the book, I highly recommend adding Toni Weschler’s book Taking Charge of Your Fertility to your reading list. She does a fantastic job presenting fertility awareness information in an informative and engaging way. Much of what I first learned about STM was learned using her text, and I cannot recommend it enough for those just starting out.

Or, if you find yourself utterly lost and confused (or simply wanting a bit of guidance) after reading this book, there are many wonderful menstrual health and fertility awareness resources who can help guide you on your journey!

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