Physiology of Normal Labor and Delivery 10. Maternal Physiology and Prenatal Care 11. Clinical Genetics 12. Infectious Diseases and AIDS 13. Although puberty occurs when increased gonadotropin secretions by the pituitary stimulate the gonads, the stage has been set during fetal life.
Gonadotropins become sensitive to estrogen feedback suppression and fall to undetectable levels.
Neonatal Life Immediately after birth, the stimulatory effect of hCG on the male testis, and the suppressive effect of placental estrogens and progesterone on the pituitary and hypothalamus are withdrawn, leading to a rapid rise in gonadotropins. The withdrawal of placental hormones may actually lead to scant vaginal bleeding in females as well as temporary nipple discharge. The subsequent pattern of gonadotropin hormone levels and gonadal response differs in infant boys and girls. In girls, there is a fall in estradiol levels in the first week of life, and then a gradual minimal rise that continues for one to two years. In boys, testosterone levels rapidly decrease in the first week of life, and then increase to pubertal levels for two to four months before declining.