These fertility awareness models actually can work, and work well. A recent 20-year German study asked 900 women to track their fertility every day by monitoring their body temperature and cervical mucus, and use that information to avoid pregnancy. The study’s researchers found this to be 98.2 percent effective—comparable with the pill, and a far cry from the 82 percent effectiveness rate of the withdrawal method.

In January, a group of physicians organized through the Family Medicine Education Consortium published a review looking into the efficacy of various FABMs. They combed through all the relevant research published since 1980, and concluded that “when correctly used to avoid pregnancy, modern fertility awareness-based methods have unintended pregnancy rates of less than five (per 100 women years).” (A woman year is one year in the reproductive life of a woman.) Their effectiveness levels, in other words, are “comparable to those of commonly used contraceptives,” the study’s authors add.

Modern fertility-awareness methods are rooted in an ever-improving understanding of the various subtle signs a woman’s body flashes to indicate it’s in prime baby-making mode. Some FABMs teach women how to chart cervical mucus secretions—and their changes in quantity and texture—to figure out when she’s fertile. Other approaches add the requirement that practitioners record their daily basal body temperature. Still others combine mucus observations with technology that picks up on hormones associated with fertility in urine.

The downside is that all FABM methods require in-person training, generally multiple sessions (reading a book or consulting a website or an app doesn’t quite cut it). Plus, the few minutes it takes to measure and chart symptoms each day makes the methods much more user-dependent than all of the more popular forms of contraception.

The distinction between these newer versions of FABM and older vintages, like the outmoded rhythm method, which has women count days on a calendar rather than look for bodily signs of fertility, can be lost on the uninformed. The Centers for Disease Control and Prevention’s periodic contraception report, for example, lumps together all natural approaches—including the rhythm method—and stamps them with a damning 24 percent failure rate. (A full 86 percent of the natural-method users surveyed for that report, in fact, said that rhythm was their go-to model.)

But this is the least of FABMs’ obstacles to wider adoption. A much more complicated tangle of factors must be called up in explaining this paradox in which a sizable proportion of women have expressed a desire for a viable birth control option that practically no one uses.

There’s the obvious image problem, for a start. FABM is the secular branch of a much older—and thoroughly Catholic—tree called Natural Family Planning (NFP). Like FABMs, NFP methods also teach cervical mucus observation and temperature-taking, but they preach abstinence during fertile times, so that a couple never has to use any barrier methods like condoms, diaphragms, or spermicide. FABMs generally advise the use of two barrier methods if a couple decides to have sex while the woman is most fertile.