Pituitary responses in LH secretion to LHRH during pregnancy.

Thirty-six pregnant women and 15 normally menstruating women were each given 100 microng of synthetic luteinizing hormone releasing hormone (LHRH) by a single intravenous injection. Human chorionic gonadotropin (hCG), luteinizing hormone (LH), and follicle stimulating hormone (FSH) levels were determined by specific radioimmunoassay (RIA) technics. For the determination of the serum LH levels, the LHbeta-RIA method, which is unaffected by hCG at sample levels as high as 500 IU/ml, was used. Serum concentrations of LH and FSH were lower in pregnant women than in the normal women in the follicular and luteal phases. While the release of LH was observed in pregnant women following the administration of LHRH, the average net increase was less than that seen in both the follicular and luteal phases. During pregnancy, there was a progressive decrease in the LH response to LHRH, but no release of FSH.