Studies on the gonadotropin response after administration of LH/FSH-releasing hormone (LRH) during pregnancy and after therapeutic abortion in the second trimester.

The gonadotropin response to synthetic LH/FSH-releasing hormone (LRH) was found to be suppressed in the second trimester of pregnancy. The basal levels of plasma FSH were very low and no detectable increase occurred after injection of up to 500 mug LRH intravenously. Five of the women were then tested with 25 mug of LRH intravenously on three occasions during the first month after therapeutic abortion in the second trimester. A rapid normalization of the basal plasma levels of FSH and LH and of the response to LRH occurred. This is in contrast with the pattern after term pregnancy. The possible role of different hormones and of the duration of pregnancy (duration of inhibition) as an explanation for this discrepancy are discussed.