AMH and premature menopause: Group 1: Good ovarian reserve with normal or only slightly reduced AMH levels; Group 2: Borderline/low ovarian reserve with AMH levels just above the lower detection limit and still regular menstrual cycles; Group 3: Very low ovarian reserve and premature ovarian insufficiency (POI) with undetectable AMH concentration, elevated serum FSH concentration and oligo/amenorrhoea.