(STAT News) – Menstruation is a critical indicator of health. Whether and when someone with a uterus gets their period — for the first time, and throughout their life — can reflect not only their reproductive health, but their risk of cardiovascular disease, cancer, miscarriage, and premature death. That also makes menstruation a useful measure of population health. And digital tools for clinical research are beginning to shed light on just how significantly periods are changing over time.

A study published Wednesday in JAMA Network Open, based on data from more than 71,00 women collected through the Apple Research App, shows that girls in the United States have been getting their first period earlier and earlier over the last 55 years–and it has taken longer for their periods to become regular, pointing to worsening overall reproductive and population health. (Read More)