Sites listed here and in the subcategories will contain largely non-commercial information about one or more aspects of menstruation. Commercial sites (such as those for drug companies or health services) may be suitable additions to the category if they contain significant unique information that does not focus on the product or service.
Amenorrhea is the absence of periods in matured woman, who is neither pregnant nor past menopause. It comes in two types, primary (never had a period) and secondary (had periods, then they stopped).