When I checked the documentation for HealthKit […] I was disappointed to find out that Apple did not include anything related to menstruation and the reproductive health of roughly half of the world’s population.
In case you’re wondering whether Health is only concerned with a few basics: Apple has predicted the need to input data about blood oxygen saturation, your daily molybdenum or pathogenic acid intake, cycling distance, number of times fallen and your electrodermal activity, but nothing to do with recording information about your menstrual cycle.