Failure of withdrawal bleeding during combined oral contraceptive therapy: "amenorrhoea on the pill".

Serum follicle stimulating hormone, luteinising hormone and oestradiol-17beta concentrations have been measured in 21 patients with failure of withdrawal bleeding during combined oral contraceptive therapy and 21 matched controls with a normal bleeding pattern. Gonadotrophin and oestradiol-17beta concentrations were effectively suppressed in all patients during the phase of contraceptive ingestion. During the week between courses of treatment, there was a significant rise in the gonadotrophin (p less than 0.02) and oestradiol (p less than 0.05) concentrations in the patients but not in the controls. It is suggested that patients with failure of withdrawal bleeding during combined oral contraceptive therapy may have higher total oestrogen levels during the treatment-free week because of a less persistent suppression of hypothalamic-pituitary-ovarian function.