Testosterone, estradiol, 170H-progesterone, and androstenedione (except in cord samples) concentrations were determined in cord sera (30 male and 14 female) and in peripheral sera from infants (121 male and 110 female), age 1 day to 2 years. Male and female cord serum levels of these steroids were not significantly different. In both sexes levels during the first week were lower than those in cord sera. In male infants serum testosterone and 170H-progesterone levels rose sharply in the second week of life, reached a peak at 1-2 months, and then declined to the range seen in later childhood by 6 months of age; male serum androstenedione and estradiol concentrations were higher during the first 2 months of life, but no distinct pattern of rise and fall was seen. In girls serum testosterone levels fell in the first week to the range seen throughout childhood; serum concentration of estradiol, androstenedione, and 17OH-progesterone in girls were markedly variable, with many values above the childhood range being seen, particularly in the first 6 months. These data provide further evidence of active Leydig cell function in male infants. They suggest that there is also ovarian secretion of sex steroids in some female infants in response to the elevated FSH and LH levels which are seen at this time.

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Mixed cord sera (27 male, 28 female) and sera from 105 male and 93 female children aged 5 days to 4 yr were assayed for FSH, LH and hCG. Cord hCG was similar in both sexes (median 58 mIU/ml; range 20-9000), and fell to less than 5 mIU/ml by 5 days of life, a value which is below the limit of detectable cross reactivity in the LH radioimmunoassay. Cord FSH was less than 5.5 mug LER-907/100 ml in both sexes. In boys there was a rapid rise of FSH in early postnatal life, with peak levels up to 55 mug/100 ml between 1 week and 3 months, followed by a decline by 4 months reaching the low values seen in older prepubertal subjects. This postnatal FSH rise was both more marked in females with peak values at 2-3 months up to 169 mug/100 ml, and also more sustained with levels staying above those of older prepubertal children until 4 yr of age. Serum LH levels in the boys were in the adolescent range by 1 week of age, peaked at 1 month and then declined to the usual childhood range by 4 months. A similar pattern, though with lower peak LH values, was seen in the female infants. A longitudinal study of serum FSH and LH values in one male and one female chimpanzee from 17 to 456 days of age showed patterns in serum gonadotropins which paralleled those seen in the human cross-sectional study.