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Plasma testosterone (T) was measured by a sensitive radioimmunoassay method in 143 normal newborns and infants. In cord blood T levels are significantly higher in male than in female newborns. In male infants there was an increase of T concentration from birth to the 2-3th months of life, followed by a gradual decrease. After the 7th month values observed reached those of prepubertal boys. In females the pattern was very different. T levels dropped rapidly from birth to the second week of life reaching values similar to those of prepubertal girls.
Forest et al. (1973) studied this question.