Pattern of plasma testosterone and delta4-androstenedione in normal newborns: Evidence for testicular activity at birth.

Plasma testosterone (T) and delta4-androstenedione (delta) levels were measured by a sensitive and specific radioimmunoassay method in 157 blood specimens from normal neonates. In both sexes at birth plasma T and delta were significantly higher in peripheral than in cord blood and drop within the first week of life. In males a secondary increase in both T and delta had occurred by the 2nd week of life while values continue to decrease in females. The present data demonstrate that testicular activity is still present at birth and suggest that the transient fall in T levels likely due to the removal of chorionic gonadotropin (hCG) secretion is responsible for the secondary activation of the hypothalamic pituitary axis by a negative feed-back mechanism.