Serum inhibin B in normal term-born male and female neonates during the first week of life

Inhibin B. a gonadal peptide regulating follicle stimulating hormone (FSH) secretion in adults, has been found during gestation in amniotic fluid, but at birth only in term cord blood of male babies. Since no data are availab le on the evolution of serum inhibin B during the Ist week of life, we stud ied changes in inhibin B using a specific and sensitive immunoassay in male and female neonates during the Ist week of life in relation to FSH and to evaluate the possible effect of perinatal factors on inhibin B production. Inhibin B was measured by a specific monoclonal enzyme-linked immunosorbent assay. Inhibin B was detectable in cord blood of all eight longitudinally studied male newborns, correlated negatively with the ponderal index and in creased significantly on day 5 (from 54.2 +/- 18.5 to 100.4 +/- 34.8 ng/l, P < 0.005). Cord blood inhibin B was detected in only 1 out of 13 screened female neonates. In 48 at term-born females in whom inhibin B was measured on the 5th day of life, only 20 cases had a detectable level (between 8 and 68.6 ng/l). Inhibin B concentrations in cord blood and on day 5 were indep endent of duration of pregnancy, type of delivery, Apgar score and FSH conc entration. Conclusion A sexual difference in serum inhibin B is already present at the end of gestation and changes in inhibin B during the 1st week of life are independent of follicle stimulating hormone changes and perinatal factors i n both sexes. Our data suggest that neonatal inhibin B could be used to stu dy whether the newborn has functional testes, i.e. in babies with ambiguous genitalia and/or bilateral cryptorchidism.