https://techcrunch.com/2022/09/07/apple-watch-temperature-sensor/

A lot of doctors consider body temperature – and changes in body temperature – a vital sign. That’s true both to track illnesses, but also natural processes in the body, such as ovulation data and menstrual cycle tracking.

Apple added cycle tracking three years ago, and in today’s event, it shared that it has helped 10s of millions of people gain deeper insights into their menstrual cycles and overall health.