Inhibin in normal and abnormal pregnancy: Maternal serum concentration and partial characterization

OBJECTIVE: This study evaluated maternal serum inhibin concentration and molecular distribution in normal and abnormal pregnancies. STUDY DESIGN: Serum inhibin levels were measured by radioimmunoassay in 33 abnormal pregnancies (23 singleton are 10 multiple gestations) and 33 matched controls and were compared with pregnancy variables. RESULTS: In the controls serum inhibin concentrations rose with gestational age (correlation coefficient 0.358, p< 0.01) and were higher in mothers with female fetuses (p< 0.05). Inhibin levels were higher in the abnormal singleton pregnancies (2.69 + 1.41 ng/ml) than in controls (1.26 ± 0.32 ng/ml, p< 0.0001) and increased more rapidly with gestational age in multiple pregnancies (p< 0.05). Gel filtration chromatographic analysis of immunoreactive inhibin revealed three peaks with the major form having an apparent molecular weight of 55 to 60 kd. CONCLUSIONS: Maternal serum inhibin concentrations are affected by gestational age, fetal gender and complications of pregnancy. Most of the immunoreactive inhibin in maternal circulation is a large-molecular-weight form.