SEX-DIFFERENCES IN UMBILICAL-CORD SERUM LEVELS OF INHIBIN, TESTOSTERONE, ESTRADIOL, DEHYDROEPIANDROSTERONE-SULFATE, AND SEX HORMONE-BINDINGGLOBULIN IN HUMAN TERM NEONATES

The contribution of the fetus to inhibin production in human pregnancy is unclear. Previous studies have reported inhibin concentrations in cord blood but on limited sample numbers. The present study is a more extensive examination of sex differences in immunoreactive inhibin and steroidal hormones in term umbilical cord blood. Venous serum concent rations of inhibin were found to be significantly higher in males (mea n +/- SD 2,168 +/- 914 pg/ml, n = 62) than in females (1,761 +/- 951 p g/ml, n = 63) (p < 0.01). Male concentrations of total testosterone (p < 0.005), free testosterone (p < 0.005), and estradiol (p < 0.05) wer e also significantly higher. The concentration of dehydroepiandrostero ne sulphate (DHEAS) and the sex hormone-binding globulin (SHBG) capaci ty were similar in males and females. Multivariate regression analysis showed that the inhibin concentration in males correlated with the te stosterone concentration and in females it correlated not only with te stosterone concentration but also with gestational age at delivery and SHBG capacity (all p < 0.001). Inhibin concentrations in cord arteria l serum in a subgroup of 24 males and 31 females were higher than in t he venous serum in both sexes but the differences were not statistical ly significant. Concentrations of DHEAS determined in 22 female cord a rterial blood samples(6.0 +/- 2.5 mu mol/l) were significantly higher than the venous concentrations(5.2 +/- 1.8 mu mol/l) (p < 0.05). Inhib in did not correlate with DHEAS either in their arterial serum concent rations or in the arteriovenous concentration differences. The finding s of this study are consistent with the placenta being the principal s ource of inhibin circulating in the human fetus in late pregnancy. Fur ther, they suggest that there are minor sex differences in placental m etabolism of inhibin and the steroidal sex hormones.