Biology of the neonate vol:61 issue:3 pages:150-155
Serum levels of immunoreactive inhibin, follicle-stimulating hormone (FSH), and luteinzing hormone (LH) were determined in 112 fetal cord blood samples obtained at birth between 26 and 40 weeks of gestation. High levels of inhibin immunoreactivity were detected in all samples. Between the gestational age of 26 and 28 weeks, the levels (mean +/- SE) were higher (p < 0.05) in male (21.6 +/- 1.0 U/ml; n = 12) than in female (12.8 +/- 0.2 U/ml; n = 12) fetuses. With ongoing gestation, the serum inhibin immunoreactivity decreased and was found to be similar in male (12.1 +/- 0.3 U/ml; n = 13) and female (9.1 +/- 0.7 U/ml; n = 8) fetuses at term. Serum FSH and LH levels were elevated at the beginning of the 3rd trimester of pregnancy and decreased with ongoing gestation to undetectable values at term birth. Between 26 and 32 weeks of gestation, the FSH levels were higher in females (p < 0.02), whereas the LH levels were higher in males (p < 0.01). These observations suggest that in the human fetus the pituitary-gonadal axis is active and presents sexual dimorphism; both characteristics are pronounced early during the 3rd trimester of gestation and decrease towards term.