https://www.vice.com/en_us/article/qjkpbq/period-tracking-apps-data-privacy-safety

After the fall of Roe on Friday—the 1973 decision that legalized abortion in the United States—people online started urging others to delete their period tracking apps.

Generally, apps that track menstruation and fertility extract a lot of data from users that previously only a gynecologist got in this much detail. Depending on the app, this can mean scads of information each month about when a period starts, stops, or is interrupted or unusual in some way, the heaviness, lightness, and all kind of other physical qualities of one’s blood. Some apps allow users to track what they were eating, drinking, smoking, and feeling during their period or in the weeks before and after. Some apps also allowed users to track sleep habits, whether they traveled and where, and the list goes on. It’s a treasure trove of personal data.