Menstrual Cycle

How progesterone raises your waking temperature after ovulation, why the rise confirms ovulation only after it's happened, how to take a reading that's comparable, and how it compares with a wearable's wrist temperature.

What anti-Müllerian hormone measures, why it predicts response to IVF but not your chance of conceiving naturally, what a large study found, and how to read a result.

Why watches and rings report temperature as a change from your own baseline, what moves it, how it follows the menstrual cycle and illness, and why it isn't a thermometer.

FIGO's definitions of a normal cycle (24 to 38 days) and period (up to 8 days), how much cycles vary from month to month, what data from 600,000 cycles shows, and when to see a doctor.

What studies of calendar methods and cycle apps found, why ovulation day varies so much even in regular cycles, and why a predicted fertile window isn't contraception.