According to the Rotterdam criteria, how many features are required to diagnose polycystic ovary syndrome (PCOS), and what are they?

Answer: C. Two of three: clinical/biochemical androgen excess, oligo/anovulation, polycystic ovarian morphology on ultrasound (after excluding other causes)

Diagnosing PCOS (Rotterdam criteria)

PCOS is diagnosed when two out of three of the following are present, after excluding other causes:

1. Clinical and/or biochemical androgen excess - hirsutism, acne; raised testosterone.
2. Oligo-ovulation or anovulation (oligo/amenorrhoea).
3. Polycystic ovarian morphology on ultrasound - originally >=12 follicles (2-9 mm) per ovary and/or ovarian volume >10 ml (the 2018 update used 20 follicles per ovary as the cutoff).

Exclusion of mimics

Before diagnosing PCOS, exclude late-onset congenital adrenal hyperplasia, androgen-secreting tumours, Cushing's syndrome and androgenic drug use.

Why not the others

It is not all three (any two suffice), nor any one alone; a raised LH:FSH ratio or polycystic ovaries on ultrasound alone is insufficient - polycystic morphology can occur in women without the syndrome.