A longitudinal study of maternal serum inhibin-A inhibin-B, activin-A activin-AB, pro-αC and follistatin during pregnancy

Maternal serum concentrations of inhibin-A, inhibin-B, activin-A, activin-AB, pro-αC-related inhibin forms, total follistatin, steroids and gonadotrophins were measured longitudinally in six normal singleton pregnancies. Maternal venous blood was collected randomly during a spontaneous follicular phase prior to donor insemination, at 5, 7, 9, 11, 16, 20, 24, 28, 32 and 36 weeks after the first missed menses and in the early puerperium. Steroid and gonadotrophin profiles conformed to previous reports. While at week 5 of gestation inhibin-A, activin-A and follistatin concentrations were similar to those at the follicular phase, all three increased progressively (P < 0.001) to maximal concentrations in week 36: ~48-fold (3740 ± 1349 ng inhibin-A/ml), ~22-fold (6109 ± 1443 ng activin-A/ml) and ~10-fold (3563 ± 418 ng follistatin/ml) higher. Pro-αC concentrations reached a maximum in weeks 5 (~5-fold, P < 0.001) and 36 (1027 ± 174 pg/ml, P < 0.01). Inhibin-B (71 ± 23 pg/ml prior to pregnancy) was undetectable (< 12 pg/ml) between week 5-16 of gestation but increased slightly in the third trimester (26 ± 7 pg/ml in week 36). Activin-AB was undetectable throughout pregnancy. Post-partum concentrations of inhibin-A (41 ± 12 ng/ml), inhibin-B (< 12 pg/ml), activin-A (950 ± 149 pg/ml), pro-αC (128 ± 22 pg/ml) and follistatin (990 ± 79 ng/ml) were substantially lower than at week 36 of gestation. The activin-A:follistatin ratio increased from 0.5 in week 5 to 1.8 in week 36, suggesting that more free activin-A is available in the maternal circulation during late pregnancy.