Gonadotropins, Prolactin, Inhibin A, Inhibin B, and Activin A in Human Fetal Serum from Midpregnancy and Term Pregnancy

Using specific enzyme-linked immunosorbent assays we measured inhibin A, inhibin B, and activin A in relation to LH, FSH, and PRL in normal human fetal midpregnancy serum obtained by in utero cord venipuncture (n = 25) and compared these results to those in fetal serum from term pregnancies (n = 23). We also tested serum from fetuses with intrauterine growth retardation (n = 6) or trisomy 21 (n = 6). We found no measurable inhibin A, except in three midpregnancy males (3 of 14). Inhibin B, however, was detected in midpregnancy male fetuses (167 ± 67 pg/mL) and was higher than that in females (16 ± 12 pg/mL). It was present in male term fetuses (125 ± 32 pg/mL), but not in females. The activin A levels did not significantly differ between term and midpregnancy males and females. LH and FSH were detected in midpregnancy male fetuses (4.4 ± 3.3 and 0.77 ± 0.49 mIU/mL, respectively), with higher levels in females (33.0 ± 23.2 and 54.4 ± 27.7 mIU/mL, respectively), and were suppressed at term. PRL did not exhibit sexual difference, but showed a higher level at term (322.4 ± 113.8 ng/mL) than at midpregnancy (33.0 ± 26.1 ng/mL). Comparison of inhibin B with FSH levels showed correlation coefficients of −0.565 at midpregnancy vs. +0.445 at term. Serum from fetuses with intrauterine growth retardation or trisomy 21 did not show any different hormonal profiles. These data suggest that inhibin B is probably an additional factor in FSH inhibition at midpregnancy, whereas activin A is not associated with any change in the different studied populations. We speculate that inhibin A could be a method to detect maternal blood contamination in cord venipuncture.