Role of pituitary ovarian axis in physiologic puerperal infertility

Although the puerperal ovarian response to exogenous gonadotropins is reportedly reduced and pituitary insensitivity to subcutaneous LH RH has been described, inconsistencies in these data led to a reevaluation of the postpartum pituitary ovarian axis under a standardized methodology. I.V. LH RH (100 μg) administered to parturient lactating (L) and nonlactating (NL) women in the first 20 postpartum days failed to provoke an increase in plasma LH and FSH. On the other hand, between 35 and 80 postpartum days, significant increments were observed (hLH: 12.0 ± 1.5 mIU/ml [s.e.] to 62.1 ± 8.1 mIU/ml and hFSH: 7.9 ± 0.8 mIU/ml to 15.9 ± 3.7 mIU/ml). These changes were followed by increases in plasma estradiol and a fall in plasma progesterone within 48 hours. I.M. hMG (Pergonal 150 units) produced a 2-3 fold increase in mean plasma estradiol regardless of the postpartum interval. Plasma progesterone also rose, more so in (L). Basal plasma prolactin was higher in (L) than in (NL) but remained unchanged after each exogenous stimulus. While a diminished pituitary response follows the I.V. injection of gonadotropin releasing hormone, ovarian responsiveness to gonadotropins remains intact. The data suggest that ovarian activity in terms of steroid production is related merely to the concentration of circulating gonadotropins. Gonadotropin levels are low for a finite period postpartum due perhaps to an altered pituitary responsiveness to endogenous LH RH. The absence of significant gonadotropin response differences between lactating and nonlactating women in the first postpartum days raises speculation as to the role of nursing in the maintenance of postpartum infertility.