March 1, 2024

Cycle Tracking

The real pièce de résistance for me, however, is the updated cycle tracking on this version of the Apple Watch. You’ve always been able to track your period using the Health app, but now there are two sensors within the watch that track your temperature while you sleep to help estimate when you’re ovulating. This is far more advanced than previous versions, and also could be used for tracking fertility.

In order to accurately predict ovulation, you need to monitor your basal body temperature, which is your body temperature when you are completely at rest.

Your basal body temperature rises by half a degree or less when you ovulate and stays elevated for the second half of the menstrual cycle. Many things, including lack of sleep, alcohol consumption, or even physical activity can influence body temperature. If you’re using a traditional basal body temperature thermometer (a special type that allows you to measure very small fluctuations, down to one-tenth or one-hundredth of a degree), you have to get the reading immediately after you wake up, before any physical activity takes place. So basically you can barely move until you’ve measured your temperature. Every morning.

Also, you’re most fertile around two to three days before your temperature rises, so you don’t really know until after the fact that conditions were ripe for procreation. The whole idea is that if you’re diligent enough month after month, you’ll be able to predict which days you’ll be fertile based on previous rises and falls in basal body temperature.

In theory, this method could be used for birth control by avoiding sex during the fertile window, although it sounds a bit terrifying and chaotic to me personally. (Apple specifically says the Cycle Tracking app should not be used as a form of birth control or to diagnose a health condition.)

However, if there’s one thing I learned during my search for a good nonhormonal birth control option, it’s that it’s not easy to find a contraceptive method that works for you. I can appreciate that some people may use the temperature method, in general, to prevent pregnancy, despite the questionable reliability, because there are honestly so many pros and cons to every single method. (It’s one of the least reliable methods of birth control; 1 in 4 people who use it as a contraceptive method for a year experience a pregnancy.)

It’s no secret that I landed on a copper IUD for long-term contraception, and that I have no plans to remove it any time soon, but I can see how helpful the tracking feature could be for family planning. Wearing the watch to bed every night allows it to gauge your basal body temperature, which may have a lower risk for human error than using a thermometer while remaining as still as possible before your morning pee. It’s not the most comfortable to sleep in at first, but if you’re using this functionality, it’s worth getting used to. (You have to wear the watch for five nights to get wrist temperature data and two menstrual cycles to get retrospective ovulation estimates; these functions are also not available in every country.)

The temperature readings help the watch and your Health app get to know your cycle and alert you with predictions for when you’ll be ovulating or get your period. You can even download your cycle data in a PDF chart to send to your doctor at any time.

Period tracking and all other reproductive health data have become riskier after the overturn of Roe v. Wade, so privacy is of course a concern. Apple says that all health data is encrypted on your devices and only accessible to others with your permission. (You can also turn off the wrist temperature tracking function.)


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