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An Expert’s Look at Fertility Awareness Methods
What you should know if you’re considering this kind of contraception
In 2018, the United States Food and Drug Administration (FDA), for the first time, approved an app for use as a contraceptive method. The app, called Natural Cycles, uses an algorithm that aims to predict the days of the month a woman is likely to be fertile based on daily basal body temperature readings and menstrual cycle information (and optionally, results from a home test kit measuring luteinizing hormone in urine). The approval sparked conversation around how people are using fertility awareness-based methods (FABMs) to prevent pregnancy today, and what options are available to them.
Currently, only about 3% of women who use contraception in the U.S. use an FABM. And while there’s a misconception that “fertility awareness-based method” only means the rhythm method, the reality is that there are many different FABMs, some with more evidence than others.
These methods are based on the fact that sex can only lead to pregnancy during approximately six to nine days of each menstrual cycle, sometimes called the “fertile window.” FABM users track changes in one or more fertility signs — menstrual cycle dates, basal body temperature, cervical mucus or position, and hormone markers in urine — as a way to attempt to identify when they are fertile each month. During potentially fertile days (a span of time that is usually longer than the actual six to nine day fertile window), users wishing to avoid pregnancy either abstain from penile-vaginal sex or use an additional method, like a condom.
Unfortunately, misinformation about FABMs is rampant, and even the available research on these methods leaves a lot to be desired. In 2018, my colleagues and I published a systematic review which gathered all published prospective studies on FABM effectiveness and evaluated the quality of each. None of the studies we found qualified as “high quality.” (More on our systematic review below.) Some companies are also using flawed data to market their method. For example, a company that manufactures a $330 thermometer called Daysy claimed that it was 99.4% effective in preventing pregnancy. However, this claim was based on poor study practices, and ultimately, the company’s…
