Serum Bioactive Follicle-Stimulating Hormone-Like Activity Increases during pregnancy

Abstract

It is presently accepted that high circulating steroid levels during pregnancy suppress pituitary immunoreactive FSH (I-FSH) secretion from early pregnancy to term. In this study we tested the hypothesis that bioactive FSH (B-FSH) in the sera of pregnant women would likewise be suppressed. Serum samples were obtained from one woman daily for 21 days after the I-LH surge, and in a second, every 10 min for 10 h on days 10, 20, and 27 after the I-LH surge. Single serum samples were also obtained from women at 2–41 weeks of gestation. In all samples, I-LH/hCG, I-FSH, B-FSH, progesterone (P), and estradiol (E2) were measured. In the first woman, serum I-FSH levels were suppressed from days 9–21 after the LH surge (0.2 ± 0.04 ng/mL; 1.9 ± 0.3 IU/ L), whereas serum B-FSH increased linearly from 1.7 ng/mL (5.3 1U/L) on day 9 post-I-LH surge to 6.0 ng/mL (18.6 IU/L) on day 17 (r = 0.91; P < 0.01) and remained elevated through day 21. In the second woman, the mean ± SE of the serum IFSH concentrations were 0.7 ± 0....