Role of the hypothalamic-pituitary-ovarian axis in puerperal infertility

To gain further insight into the mechanisms of postpartum infertility, plasma gonadotropins, prolactin, estradiol, and progesterone were measured following either iv LHRH or im menopausal gonadotropins (Pergonal) to postpartum women. Plasma estradiol and progesterone rose significantly between 24-72 hours following hMG injection. The response was similar in both nursing and non-nursing women throughout the intermediate and late postpartum study interval. No gonadotropin response was observed following LHRH injection in the early puerperium. Beyond five postpartum weeks, a significantly greater response following LHRH was observed in nursing compared with non-nursing women. A subsequent and significant rise in estradiol correlated with the magnitude of the LHRH-induced increment. Basal prolactin levels in nursing women were significantly greater than in non-nursing women but were unchanged after either hMG or LHRH. We conclude that the postpartum ovary is not refractory to either direct exogenous gonadotropin stimulation or to endogenously released gonadotropins, at least as far as estrogen production is concerned. Furthermore, the difference in the pituitary response to LHRH in nursing and non-nursing women may reflect a difference in the hypothalamic-pituitary axis. Elevated prolactin secretion in response to nursing may be involved in postpartum infertility, but the specific role remaine unclear.