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

Maternal serum concentrations of inhibin-A, inhibin-B, activin-A, activin-A B, pro-alpha C-related inhibin forms, total follistatin, steroids and gonad otrophins were measured longitudinally in six normal singleton pregnancies. Maternal venous blood was collected randomly during a spontaneous follicul ar phase prior to donor insemination, at 5, 7, 9, 11, 16, 20, 24, 28, 32 an d 36 weeks after the first missed menses and in the early puerperium, Stero id and gonadotrophin profiles conformed to previous reports. While at week 5 of gestation inhibin-A, activin-A and follistatin concentrations were sim ilar to those at the follicular phase, all three increased progressively (P < 0.001) to maximal concentrations in week 36: similar to 48-fold (3740 +/ - 1349 ng inhibin-A/ml), similar to 22-fold (6109 +/- 1443 ng activin-A/ml) and similar to 10-fold (3563 +/- 418 ng follistatin/ml) higher Pro-alpha C concentrations reached a maximum in weeks 5 (similar to 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 hut increased slightly in the third trimester (26 +/- 7 pg/ml in week 36). Act ivin-AB was undetectable throughout pregnancy. Post-partum concentrations o f inhibin-A (41 +/- 12 ng/ml), inhibin-B (<12 pg/ml), activin-A (950 +/- 14 9 pg/ml), pro-alpha C (128 +/- 22 pg/ml) and follistatin (990 +/- 79 ng/ml) were substantially lower than at week 36 of gestation. The activin-A:folli statin ratio increased from 0.5 in week 5 to 1.8 in week 36, suggesting tha t more free activin-A is available in the maternal circulation during late pregnancy.