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

Maternal serum concentrations of inhibin-A, inhibin-B, activin-A,activin-AB, pro-alphaC-related inhibin forms, total follistatin, steroidsand gonadotrophins were measured longitudinally in six normal singletonpregnancies. Maternal venous blood was collected randomly during aspontaneous 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 theearly puerperium. Steroid and gonadotrophin profiles conformed to previousreports. While at week 5 of gestation inhibin-A, activin-A and follistatinconcentrations were similar to those at the follicular phase, all threeincreased progressively (P < 0.001) to maximal concentrations in week36: approximately 48-fold (3740 +/- 1349 ng inhibin-A/ml), approximately22-fold (6109 +/- 1443 ng activin-A/ml) and approximately 10-fold (3563 +/-418 ng follistatin/ml) higher. Pro- alphaC concentrations reached a maximumin weeks 5 (approximately 5- fold, P < 0.001) and 36 (1027 +/- 174pg/ml, P < 0.01). Inhibin-B (71 +/- 23 pg/ml prior to pregnancy) wasundetectable (<12 pg/ml) between week 5-16 of gestation but increasedslightly in the third trimester (26 +/- 7 pg/ml in week 36). Activin-AB wasundetectable throughout pregnancy. Post-partum concentrations of inhibin-A(41 +/- 12 ng/ml), inhibin-B (<12 pg/ml), activin-A (950 +/- 149 pg/ml),pro-alphaC (128 +/- 22 pg/ml) and follistatin (990 +/- 79 ng/ml) weresubstantially lower than at week 36 of gestation. The activin-A:follistatinratio increased from 0.5 in week 5 to 1.8 in week 36, suggesting that morefree activin-A is available in the maternal circulation during latepregnancy.