Comment by dragonwriter

Pregnancy (even without elective abortion!) has a variety of risks of criminal prosecution in the post-Dobbs world, and prosecutors in some states where this is the case have expressed desire to use menstrual data to identify targets for investigation.

There's also sometimes significant risks of nongovernmental (particularly family and intimate partner) violence associated with situations that can be inferred from that data, which is one reason people often conceal things which might be inferred from it from selected other people.