In simple terms: a girl’s first menstrual period.
Why it matters for PCOS
Menarche is a girl’s first menstrual period, usually occurring around age 9 to 15, and it marks the start of menstrual cycles. In the first few years after menarche, irregular cycles are common because the hormonal system is still maturing. That is why diagnosing PCOS in teenagers calls for caution, since irregular cycles at this stage do not necessarily point to PCOS.
Clinical guidelines advise interpreting adolescent PCOS assessment in an age-appropriate way and relative to how long it has been since menarche. If irregular periods persist for several years after menarche or come with symptoms such as severe acne or excess hair growth, that is worth discussing with a doctor.
This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.