The Role of Prolactin in the Restoration of Ovarian Function During the Early Post‐partum Period in the Human Female

SUMMARY Serial plasma levels of prolactin, follicle‐stimulating hormone (FSH), luteinizing hormone (LH), 17β‐oestradiol (E) and progesterone (P) were determined by radioimmunoassay in ten healthy women during late pregnancy and puerperium until the occurrence of the first menstruation, at which moment an endometrial biopsy was taken. Prolactin concentrations, which were high during late pregnancy and the early post‐partum period, declined thereafter but remained above 30 ng/ml plasma during the period of breast‐feeding. FSH was nearly undetectable during late pregnancy and the first week post‐partum but returned to normal levels between days 7 and 18. Thereafter relatively high FSH levels were found during the period of hyperprolactinaemia. Following clearance of human chorionic gonadotrophin (HCG) during the first 2 weeks post‐partum, LH remained below the normal cyclic range in all cases for at least 28 days. Placental E and P were fully cleared within 7 days. In spite of relatively high levels of FSH, E remained low as did LH during the period of hyperprolactinaemia. Thereafter E increased followed by an increase of LH, suggesting a positive feedback of E on LH release. The first menses observed in five subjects during the study were preceded by (subnormal P levels for a relatively short period although the endometrial biopsies showed only late proliferative changes.