Studies on human sexual development. III. Fetal pituitary and serum, and amniotic fluid concentrations of LH, CG, and FSH.

Fetal sera (9-20 weeks fetal age, n = 80) and pituitary glands (9.5-20 weeks, n = 36) obtained from hysterotomy specimens, and amniotic fluids (amniocentesis; 8-40 weeks, n = 123) were assayed for FSH, LH (betaLH assay) and CG (betaCG assay). Results are expressed as mass of pure hormone. Prior to 12 weeks fetal age, pituitary, serum and amniotic fluid concentrations of LH and FSH were low or unmeasurable. In contrast, levels of CG in serum and in amniotic fluid were clearly measurable prior to 12 weeks. There was a definite CG peak at 11-14 weeks with levels up to 550 ng/ml in serum and 7400 ng/ml in amniotic fluid. Although LH levels began to rise at 12 weeks, when CG levels started to decline, serum levels of LH from 14-20 weeks in males (2-13 ng/ml) were still lower than the majority of CG levels at this time (6-115 ng/ml). These observations suggest that CG is the primary stimulus to the fetal Leydig cell which results in testosterone secretion (peak 11-17 weeks) and masculine differentiation of the genital tract. Significantly lower concentrations of both FSH and LH were observed in pituitary, serum and amniotic fluid between 12-20 weeks fetal age in males compared to females. This may be a result of feedback inhibition by the higher concentrations of testosterone in males at this time. Amniotic fluid FSH and LH concentrations correlated with their respective serum and pituitary values (P less than 0.01) indicating that amniotic fluid may provide a convenient index of fetal serum concentrations.