Apple Watch Series 8 will give users a better estimate of when they ovulated based on data from new temperature sensors.

Using two sensors on the Apple Watch Series 8, the built-in menstrual cycle tracking app will check users’ temperature at the wrist every five seconds overnight. This should allow for ovulation tracking since body temperature changes over the course of the menstrual cycle and rises in response to ovulation.

watchOS 9 and iOS 16 will also include changes to the cycle tracking app that flag any abnormalities in a user’s menstrual cycle based on the data they input about their periods. Deviations from someone’s normal cycle — like more spotting than usual — can be a signal of health conditions like fibroids or polycystic ovary syndrome (PCOS), Sumbul Desai, vice president of health at Apple, said during the launch event.

Apple is pitching its ovulation detection feature as a way to help people who are trying to get pregnant. “If you’re trying to conceive, knowing if and when you ovulated can inform your family planning with your healthcare provider,” Desai said.

People who use temperature information as a way to predict when they’re most likely to get pregnant usually have to take their temperature manually. Apple Watch would do that automatically — similarly to how the Oura Ring collects temperature and other types of user data to predict when someone might start their period.

This type of temperature-based cycle tracking and ovulation detection is also often used as a way to prevent pregnancy. It can work well if it’s done correctly, but it’s tricky to get right and isn’t a good method for people with irregular cycles.

Apple’s feature can’t be sold as a way to prevent pregnancy because it isn’t Food and Drug Administration-approved as a birth control. But the new features are inching closer to similar tech that is allowed to be marketed as birth control. For example, the app Natural Cycles was controversially cleared by the FDA in 2018 as a birth control. It uses body temperature and cycle tracking information to predict the times of a month when someone is most likely to become pregnant and lets them know to use condoms or abstain from sex.

Natural Cycles also has FDA clearance to use information from wearable devices to make its predictions. It currently accepts temperature information from the Oura Ring. Natural Cycles has discussed the potential to pull in information from the Apple Watch as well, spokesperson Lauren Hanafin said in an email to The Verge. The company would first have to run validation tests before that could happen, and the use case would depend on how accurate it is, she said.

It’s also notable that Apple is adding cycle tracking features — which could theoretically be used to tell if someone is or has been pregnant — in the few months after the Supreme Court ended federal protection for abortion. Experts haven’t seen cycle tracking information used to prosecute people suspected of having abortions in places where it’s no longer legal, but that’s still a possible risk.

Cycle tracking data on Apple devices is encrypted, and Apple cannot decrypt or read it, Desai said during the event. “Your health data is yours and yours alone,” she said.

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