Changes of serum gonadotropin levels and sex differences in premature and mature infant during neonatal life.

We measured FSH and LH concentrations by RIA in 130 cord sera and 213 peripheral sera obtained as serially as possible from 67 infants who were 5-75 days old and were born between the 28th and 42nd gestational weeks. Cord serum FSH and LH (+hCG) levels were 3.9-13.6 mIU/ml and 43.3-88.6 mIU/ml, respectively; they decreased with advancing gestational age. Postnatal FSH levels in male infants maintained low levels (3.7-8.7 mIU/ml). However, those in female infants increased with peak levels (51.8-270.3 mIU/ml) between 11 and 30 days after delivery, and then decreased; the surge was more marked and prolonged in preterm infants than in term infants. Postnatal LH levels in both sexes decreased rapidly after birth, which may be due to a decrease of placental hCG, and thereafter displayed patterns similar to FSH levels. We found a significant sex difference of serum gonadotropin levels in newborn infants and differences between term and preterm infants. Our results suggest that the sex difference of pituitary gonadal function exists and that the function matures during the fetal and neonatal life.