Serum activin A and follistatin concentrations during human pregnancy: a cross-sectional and longitudinal study

Activin A, a dimer of the beta(A)-subunit of inhibin, has been shown to hav e multiple biological activities and sites of production. Follistatin is a high-affinity binding protein for activin, which neutralizes its activity. This study provides the first data, using a cross-sectional design, on the measurement of both these proteins in the maternal circulation of a large c ohort of women (6-39 weeks of gestation, n = 2-20 women/time point) during normal pregnancies, and confirms that similar patterns are seen in nine wom en studied longitudinally during pregnancy. The concentrations of total act ivin A were measured using a specific two-site enzyme-linked immunosorbent assay (ELISA), and a new radioimmunoassay for measuring total follistatin i n serum utilizing dissociating reagents to eliminate the interference of ac tivin is described. At 38-39 weeks gestation, both activin A and follistati n concentrations rose to a peak (4.59 +/- 0.54 ng/ml and 72.7 +/- 3.31 ng/m l, respectively). The activin A and follistatin concentrations were highly correlated both in the cross-sectional study (P <0.0001) and in individual women in the longitudinal study (P <0.05-0.0001). Concentrations of follist atin showed a greater increase in the second trimester of pregnancy relativ e to activin A concentrations. The parallel increase in the secretion of th ese two proteins throughout pregnancy probably reflects feto-placental secr etion.