Median urinary testosterone concentrations in male and female infants from 7 days to 6 months of age. Error bars represent the interquartile range. Testosterone was measured at day 7 postnatal (D7) and then monthly from 1 month (M1) to 6 months (M6) of age. Urinary testosterone was measured using HPLC-tandem mass spectrometry. Urinary testosterone concentrations are higher in boys than in girls, and testosterone peaks in boys at 1 month of age, is lower before and after this age, and declines to baseline by about age 6 months. The figure is reproduced from  by permission of Elsevier.