Serum Levels of Immunoreactive LH‐RF through Pregnancy and Parturition

Serum concentration of LH-RF during pregnancy and 4 different stages of parturition in the same subjects were measured by newly developed sensitive radioimmunoassay for LH-RF. Serum levels of LH-RF during pregnancy were markedly lower (4.4 + 1.2 pg/ml), compared to those in menstrual cycle (35.6 + 3.5 pg/ml) that were measured previously by the same radioimmunoassay for LH-RF. Among the series of 4 stages of parturition, i.e. (1) during labor, (2) immediately after delivery, (3) 10 minutes after placenta delivery and (4) 4 days after delivery, the mean values for LH-RF were found to be higher in the samples immediately after delivery (3.7 + 0.9 pg/ml) and in those 10 minutes after placenta delivery (4.4 + 0.8 pg/ml). In individual cases, however, three out of 12 women showed peaks of LH-RF level immediately after delivery and 6 out of 12 showed peaks 10 minutes after placenta delivery.