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 birth control algorithms, according to an announcement from Natural Cycles on Tuesday.
Natural Cycles is the only cycle tracking app approved by the US Food and Drug Administration for use as birth control. Unlike other period-tracking apps, NaturalCycles requires daily and highly consistent basal body temperature readings to detect ovulation and predict one’s “fertile window,” the few days when a person is able to get pregnant.
The Series 8 and Ultra models of the Apple Watch, as well as the new Series 9 and Ultra 2 watches, come with temperature sensors that can collect subtle temperature changes during your menstrual cycle, as you sleep throughout the night. Basal body temperature can also be accurately measured 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-tracking capabilities found in wearables like the Apple Watch and the Ora Ring, which Natural Cycles has also received approval to add, will make the whole process easier.
Natural Cycles co-founder and CEO Dr. Elina Berglund Scherwitzl said in a press release that the company has begun clinical trials on whether the company can use temperature data from the Apple Watch for its algorithms. And they did not disappoint.
“We were thrilled with the results, submitted them to the FDA, and with this approval are excited to give our users the ability to seamlessly measure using a device that many already own and love,” said Scherwitzl.
Importantly, the integration of Natural Cycles with some Apple Watch models does not mean that Apple’s cycle-tracking feature in the Health app should be used as contraception, or that any of its devices should be used as birth control. As the tech giant expands on its wellness, which includes a massive and ongoing study of women’s health, it’s clear that ovulation and periods are only approximate, predictable, and shouldn’t be used as birth control.
However, the fact that the only FDA-cleared birth control app is capitalizing on big-name wearables that keep improving and improving their health-tracking metrics speaks to a larger trend toward treating fertility awareness as a standard health issue. It also suggests that the sky may be the limit when it comes to accessing (and actually using) health data that has historically been difficult.
How the natural cycle works as birth control
Natural cycles work by measuring the body’s basal temperature and over a few months, it works by finding a pattern that can determine when a person ovulates and when they are likely to ovulate the following month. Before ovulation, the temperature is usually low during the first half of the menstrual cycle and rises very slightly (only a fraction of a degree) after ovulation. The algorithm collects data from the temperature you input, as well as the days you log, to begin predicting which days are likely to be fertile.
With perfect use, Natural Cycles says it’s up to 98% effective at preventing pregnancy, and less so with normal use. But the problem — and a major criticism of temperature-based birth control or cycle-tracking in general — is that it’s much harder to use “perfectly” than other forms of birth control, including pills or IUDs. Common experiences like sleeping two hours more or less than usual, drinking alcohol, and feeling sick can throw off your body temperature measurements and make the day’s data useless. Also, many people have irregular periods that can be difficult to track. (And the exact day of ovulation can vary even among people with “regular” cycles.)
For these reasons, health care providers generally recommend that people use a different form of birth control in addition to tracking their basal body temperature if they do not want to get pregnant.
However, combining temperature records with luteinizing hormone tests and cervical mucus tracking to identify fertile windows and upcoming ovulation can make methods like natural cycles more accurate.
Read further: Why Apple is moving your health information to the iPad