Thirty-seven women who allegedly relied on the European Union-certified fertility app Natural Cycles as a non-hormonal method of birth control ended up with unwanted pregnancies in the last quarter of 2017, according to the Swedish news agency SVT. Now, the Swedish hospital where these women sought abortions is flagging the app to local regulatory authorities.

The app, which is available on Google Play and Apple's App store, has more than 500,000 users in 161 countries, according to data from Natural Cycles. Its technology relies on inputing daily body-temperature readings from a thermometer to predict a user's ovulation, since body temperature rises slightly when your ovaries release an egg. (The app's algorithm also accounts for cycle irregularities and sperm survival rates, while an optional ovulation test detects the hormones released one to two days before ovulation.)

In theory, if you avoid unprotected sex for about five days before ovulation and about two days after, you can avoid getting pregnant, according to Planned Parenthood. The healthcare provider estimates tracking fertility using body temperature, changes in cervical mucus, or by estimating dates of ovulation based on when you're expecting your period (i.e., Fertility Awareness Methods or FAMs) can prevent pregnancy 76 to 88 percent of the time. By comparison, when used perfectly, which isn't always realistic IRL, condoms are 98 percent effective; IUDs are 99 percent effective; and birth control pills are 99 percent effective,according to Planned Parenthood.

The makers of Natural Cycles claim the app prevents unwanted pregnancy 93 percent of the time. Södersjukhuset Hospital in Stockholm, Sweden found that 37 of the 668 of the patients who sought an abortion between September and December 2017 had been using the app to avoid pregnancy, according to SVT.

In a statement, a Natural Cycles spokesperson wrote:

"No contraception is 100 percent effective, and unwanted pregnancies is an unfortunate risk with any contraception...As our user base increases, so will the amount of unintended pregnancies coming from Natural Cycles app users, which is an inevitable reality."

Although the company hasn't received information from the 37 women who allegedly got pregnant while using the app, "the numbers mentioned in the media are not surprising given the popularity of the app and are in line with our efficacy rates," Natural Cycles's spokesperson wrote. "We have initiated an internal investigation with our clinical department in order to confirm this."

To increase the effectiveness of any FAM, Planned Parenthood recommends combing methods by, for instance, monitoring your cervical mucus in addition to using a temperature-tracking app such as Natural Cycles. At the end of the day, FAMs still don't work as well as other types of birth control — something to keep in mind when deciding how to best protect yourself.

From: Cosmopolitan US