Natural Cycles app and temperature device (Natural Cycles AB)
13 August 2018. A mobile app for determining a woman’s fertility state on any given day was cleared for marketing in the U.S. as a birth control method. The Natural Cycles app, made by NaturalCycles AB in Stockholm, Sweden, received marketing authorization from the Food and Drug Administration on Friday, which the agency says is the first mobile app it permits to prevent pregnancies.
Natural Cycles calculates a woman’s daily fertility with an algorithm based on her body temperature and menstrual cycles. The app asks the woman to measure her basal body temperature — a more sensitive temperature measurement than regular thermometers — upon waking in the morning, where a rise in temperature of about 0.5 degrees F indicates ovulation occurred and the hormone progesterone is released. After taking these measurements for a few menstrual cycles, the app’s algorithm becomes familiar enough with the woman’s cycles to calculate days when fertility is at its peak.
These most fertile days are called “red days,” referring to the color of message on the app, when protection against pregnancy, such as condoms, are recommended. Infertile days are known as “green days,” when protection may not be required. Natural Cycles recommends a separate luteinizing hormone test for ovulation that measures the woman’s urine for this hormone that increases 1 to 1.5 days before ovulation. The company says adding a luteinizing hormone test increases the number of green days by 5 percent and helps the algorithm better predict red days for planning a pregnancy.
FDA based its authorization of Natural Cycles in part on a clinical trial of 15,570 women who tested the app for an average of 8 months over a 2-year period, out of nearly 23,000 enrolled. The app’s effectiveness for predicting fertile and infertile days was based on the Pearl Index, a standard method of measuring contraception techniques that calculates device or method failures per 100 woman using the technique for 1 year. When the app is used and pregnancies occur for any reason, including errors by the app or the users — such as having unprotected sex on a red or fertile day — the app’s failure rate is 6.5 percent. When participants use the app as directed and pregnancies occur due to an error in the app to predict an infertile day, or contraception failed on a correctly-indicated fertile day by the app, the failure rate is 1.8 percent.
FDA cleared natural Cycles for pre-menopausal women age 18 and older. The app is not recommended for women who are currently using birth control or hormonal treatments that limit ovulation, or who have a condition where pregnancy would risk her health that of the fetus. The company notes that the app does not protect against sexually transmitted diseases.
The Natural Cycles company was founded by two physicists, Elina Berglund and Raoul Scherwitzl, while working at CERN in Switzerland, but then relocated to Stockholm. FDA authorized Natural Cycles under its de novo premarket review pathway for new types of low- to moderate-risk medical devices. In addition to FDA clearance, the app previously received a CE mark which permits marketing in Europe.
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