Abstract

After 1–2 weeks of birth, a newborn experiences a surge in serum concentrations of gonadotropins and sex steroids. The gonadotropins follicle stimulating hormone (FSH) and luteinizing hormone (LH) attain peak levels at 2–3 months of postnatal life, stimulating an elevated output of sex steroid hormones (testosterone, estradiol, and inhibin B) from the gonads. This postnatal endocrine surge is sometimes called “mini-puberty” because the concentrations of both gonadotropins and sex steroids reach levels that are not seen again during childhood until puberty. The high levels of gonadotropins and sex steroids during this time provide pediatric endocrinologists with a baseline for assessing the function of the hypothalamic-pituitary-gonadal axis during infancy. The period over which these hormones remain elevated varies by hormone and by sex, but the duration of exposure is at least several months. Elevated levels of testosterone in male infants during postnatal life appear to have enduring effects on the growth of male external genitalia and on sperm production. Experiments on non-human primate males suggest that the postnatal endocrine surge may also be involved in shaping sexual motivation but not sexual orientation. Much less is known of the effects of the postnatal endocrine surge on sexual growth in females; however, it is clear that high levels of FSH stimulate follicular maturation in the ovary during the postnatal period. Some research on non-human primates also suggests that the skeletal and immune systems may be sensitive to postnatal endocrine events.