A woman who wants to track her fertility on her phone has no shortage of options to choose from: The past several years have seen a proliferation of apps with varying degrees of name cutesiness, like Flo, Clue, Glow, and Pink Pad, all promising to help users either avoid pregnancy or achieve it.
On Friday, the FDA issued its first-ever approval to one of these apps for use as contraception, called Natural Cycles. Because a woman’s body temperature increases slightly during ovulation, the app works by asking women to use a basal thermometer (which is more sensitive than a regular thermometer) to keep a daily log of their temperature, and then uses that information to flag fertile days and days when users could have sex without worrying about getting pregnant. Last year, Natural Cycles also became the first contraceptive app approved by the European Medicines Agency, the European equivalent of the FDA.
Most birth-control methods have two effectiveness rates: the one that applies in an ideal world, when people use it perfectly every single time, and the one that applies in the real world, taking into account that humans are bumbling and forgetful and mistake-prone creatures. According to the FDA, a clinical trial for Natural Cycles found it to be around 98 percent effective with perfect use and 92.5 percent effective with actual use. Fertility awareness methods in general are around 76 to 88 percent effective in preventing pregnancy; by comparison, birth control pills are 99 percent effective when used perfectly, but 91 percent effective with actual use; for condoms, those numbers are 98 percent and 85 percent, respectively. (IUDs, at more than 99 percent effective, are one of the few methods of contraception that don’t need to take human error into account — once they’re in, you don’t have to do anything.)
But while Natural Cycles may be more effective than the typical fertility awareness plan, the decision to approve it doesn’t come without controversy, and other research suggests that using it as a sole method of contraception may be a risky choice: A 2016 study in the journal Obstetrics and Gynecology found that out of 53 common fertility-tracking apps and online tools, only four could actually predict a woman’s fertile period with a high degree of accuracy, and fertility experts have argued that relying on basal body temperature is too simple a measure to track ovulation. Real-life experience, meanwhile, suggests the same thing: Earlier this year, 37 women in Sweden who used Natural Cycles reported that they’d gotten pregnant while using the app to prevent exactly that.