Gerund used as an uncountable noun denoting the process of menstruation.
Menstruating can cause cramps and mood changes.
Менструация может вызывать спазмы и перепады настроения.
menstruatinggerund / present participle Used attributively or predicatively to describe someone who is currently experiencing menstruation.
The clinic provides free products for menstruating students.
Клиника бесплатно предоставляет средства менструирующим студенткам.