How can I differentiate between primary and secondary amenorrhoea in a clinical setting?

Primary amenorrhoea is defined as the absence of menstruation by age 13 in girls without secondary sexual characteristics, or by age 15 in girls with normal secondary sexual characteristics, or if menstruation has not started within 3 years of thelarche (breast development) or 5 years if thelarche occurred before age 10.

In clinical practice, primary amenorrhoea is suspected in girls who have not started menstruating by these age thresholds and requires referral for specialist investigation.

Secondary amenorrhoea is the absence of menstruation for 3 or more months in women who previously had regular periods, or 6 months in those with previously irregular cycles.

In a clinical setting, differentiation is based primarily on the patient's menstrual history: whether menstruation has ever occurred (primary) or has ceased after established menstruation (secondary).

Additional clinical features such as presence or absence of secondary sexual characteristics, history of uterine or cervical surgery, symptoms of androgen excess, or systemic illness help guide further evaluation and referral.

Primary amenorrhoea often requires referral to paediatrics, gynaecology, or endocrinology depending on associated features, while secondary amenorrhoea management in primary care includes assessment for common causes like pregnancy, PCOS, hypothyroidism, and menopause, with referral for specialist care if indicated.

Thus, the key clinical differentiation is the age and menstrual history: no menstruation by defined ages with or without secondary sexual characteristics indicates primary amenorrhoea, whereas cessation of established menstruation indicates secondary amenorrhoea.

Referral criteria and management pathways differ accordingly.

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