Measurement of serum concentrations of inhibin‐A (α‐βA dimer) during human pregnancy

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Abstract
OBJECTIVE The alms were to measure concentrations of Inhibin-A (α-βA dimer) in peripheral serum during normal human pregnancy, to establish which molecular weight form(s) are present In pregnancy serum and to relate the concentrations of inhlbin-A to those of oestradlol and progesterone. DESIGN In a retrospective cross-sectional study 211 serum samples collected at 2-week Intervals from week 8 to 38 of gestation were analysed for inhlbln-A by enzyme immunoassay and oestradlol and progesterone by radioimmunoassay. Pooled samples corresponding to first, second and third trimester were subsequently used for fast protein liquid chromatography chromatographic analysis of Inhibln forms present. PATIENTS Blood samples were obtained from normal pregnant women attending the antenatal clinic. RESULTS Concentrations of Inhibin-A in peripheral serum gradually decreased from 1.76±0.15/μg/l in week 8 of gestation to 0.86±0.12μg/l in week 16 (PP<0.01) during the third trimester reaching a maximal value of 5.68±0.89 μg/l In week 36. Chromatographic analysis of pooled serum samples from the first, second and third trimester showed that the fully processed 31-kDa molecule is the predominant circulating form of inhlbln-A throughout human gestation. Likewise, only the 31-kDa form was Identified in extracts of term placenta which contained ∼20 μg inhibin-A/kg tissue. CONCLUSION Inhlbin-A, principally the 31-kDa form, is present in peripheral blood throughout human gestation at concentrations up to 50 times greater than maximum values found during the spontaneous menstrual cycle (∼100ng/l). The finding of highest serum values during the third trimester and of significant concentrations In term placenta firmly support a placental rather than luteal origin for this material.