Changing patterns of FSH and LH response to gonadotropin-releasing hormone in the puerperium.

Gonadotropin responses to synthetic gonadotropin-releasing hormone (GnRH or LRF), as well as basal concentrations of gonadogropins, estradiol, and prolactin, were determined at weekly intervals during the first eight weeks post partum in seven non-nursing, non-steroid-treated women. The results were compared with those of a group of eleven women studied on the second day of the menstrual cycle. In the postpartum group, baseline concentrations of LH and FSH similar to those seen in the early follicular phase of the menstrual cycle occurred by the third week post partum. In response to an iv bolus of 100 mug GnRH, elevations of serum LH: 1) occurred as early as the second postpartum week; 2) were less than those of women during the early follicular phase until the fourth postpartum week; and 3) were exaggerated (when compared with those ob subjects in the early follicular phase) during the fifth through the eighth week post partum. Similarly, the FSH responses to GnRH in the puerperium were similar to those of the subjects during the early follicular phase by the third week post partum, and were exaggerated during the second month post partum. These studies demonstrate that human pregnancy is followed by a period of relative pituitary refractoriness followed by one of increased responsiveness to GnRH.