The dramatic changes that occur in the fetus at birth are
familiar to all. They include the beginning of respiration, the
rerouting of the pulmonary circulation after closure of the
ductus arteriosus, the decline in formed elements of the blood,
and the awakening of the gastrointestinal tract and kidney, to
name a few. We are now beginning to learn of less obvious
differences between intrauterine and extrauterine life. The most
recent concern certain hormonal changes. Using rhesus monkeys in
late pregnancy, Mintz, Chez, and Horger1 have measured the
concentrations, and the responses to various stimuli, of insulin
and growth hormone in fetal and maternal plasma and in that of
the newly delivered young. Access to the fetal circulation was
effected through an incision in the abdominal wall of the
anesthetized mother and then through the myometrium and the
decidua and chorion of the placenta but not through the amnion.