If you have an Apple Watch Series 8 or Ultra and use the Natural Cycles app, you can now use temperature data from your smartwatch to feed its birth control algorithm, Natural Cycles announced Tuesday.
Natural Cycles is the only cycle tracking app approved by the U.S. Food and Drug Administration for use as birth control. Unlike other period tracking apps, Natural Cycles requires daily and highly consistent measurements of basal body temperature to detect ovulation and predict a person’s “fertile window,” the handful of days when a person can become pregnant.
The Series 8 and Ultra models of the Apple Watch, as well as the new Series 9 and Ultra2 watches come with temperature sensors that, when worn to bed at night, can sense subtle temperature shifts that occur during the menstrual cycle. Basal body temperature can also be measured accurately if taken first thing in the morning with a basal thermometer, which Natural Cycles provides with its $100 annual subscription. But the hope is that the automatic temperature reading of wearables like the Apple Watch and the Oura- ring, which Natural Cycles has also been given permission to combine with, will make the whole process easier.
Natural Cycles CEO Elina Berglund Scherwitzl said in a press release that after Apple added temperature sensors to its watches, Natural Cycles began clinical testing to explore whether data from Apple’s wrist temperature sensors could be used for its proprietary algorithm.
“We were thrilled with the results, submitted them to the FDA, and with this approval we are excited to give our users the ability to measure seamlessly using a device that many already own and love,” said Scherwitzl.
Importantly, Natural Cycles’ integration with some Apple Watch models does not mean that Apple’s cycle tracking feature in the Health app must be used as contraception, or that any of its devices must be used as contraception. As the tech giant continues to expand its wellness reach, including its vast and ongoing research into women’s health, it has become clear that the ovulation and menstruation estimates are just that, estimates, and should not be used as contraception.
However, the fact that the only FDA-approved birth control app is capitalizing on big-name wearables that continue to refine and improve their health data speaks to a larger trend toward fertility awareness as a mainstream health issue. It also indicates that the sky could be the limit when it comes to accessing (and actually using) health data that has historically been difficult to achieve.
How Natural Cycles Works as Birth Control
Natural Cycles works by collecting basal body temperature measurements and finding a pattern over a few months that can identify when a person has ovulated and when they are likely to ovulate next month. The temperature is usually lower in the first half of the menstrual cycle, before ovulation, and rises very slightly (only a fraction of a degree) after ovulation has occurred. As the algorithm collects data from the temperatures you enter, as well as your reported menstrual days and other data, it begins to predict which days are likely to be fertile.
When used perfectly, Natural Cycles says it is up to 98% effective, which means you should use it every day exactly as directed by the app. But the problem – and a major criticism of temperature-based contraception or fertility awareness methods in general – is that it is much more difficult to achieve ‘perfect’ use than with other forms of contraception, including pills or IUDs. Common experiences such as sleeping two hours more or less than normal, drinking alcohol, and feeling sick all throw off your body temperature readings and make data useless. In addition, many people have irregular menstrual cycles that may be harder to track. (And the exact day of ovulation tends to vary, even in people with very “regular” cycles, which is why it’s important to rely on other data besides counting days.)
For these reasons, health care providers have typically recommended that people use a form of birth control other than basal body temperature monitoring if they do not want to become pregnant.
However, combining basal body temperature measurements with luteinizing hormone tests and tracking cervical mucus to identify fertile periods and upcoming ovulation can make methods like Natural Cycles more accurate.
Read more: Why Apple is moving your health information to the iPad