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.