Role of inhibin in normal and high-risk pregnancy.

Inhibins are glycoprotein hormones of which there are two molecular forms, inhibin A and inhibin B. Classically, inhibin is known to have a negative feedback effect on pituitary follicle-stimulating hormone secretion. The fetoplacental unit produces inhibin throughout pregnancy. Inhibin A is the predominant molecular form of inhibin in maternal circulation from 4 weeks of gestation. Although the precise biological function of inhibin A in pregnancy is unclear, it is evident from recent studies that inhibin A could be a better marker of placental function than human chorionic gonadotropin because of its shorter half-life. The possible clinical applications for the measurement of inhibin A in early pregnancy could be in predicting miscarriage, Down's syndrome, preeclampsia, and fetal growth restriction in the first and/or second trimester before the onset of the clinical symptoms. The source of inhibins, factors controlling inhibin production, the possible functions of inhibin, and the use of inhibin measurement in normal and high-risk pregnancy are reviewed.