[Changes in human serum corticosterone and cortisol during pregnancy, labor and delivery]

Serum corticosterone and cortisol concentrations were determined during pregnancy and at delivery in six normal pregnant women. The concentrations of both steroids increased gradually during pregnancy and in late pregnancy they reached values which were 2.5 times those in early pregnancy. The corticosterone concentration increased rapidly immediately after delivery, the values averaging 6.3 times those at the onset of the first labor pain, whereas the cortisol concentration was only about 2.1 times. Although the corticosterone to cortisol concentration ratio was constantly within the normal range throughout pregnancy until delivery, a significant increase in the ratio was observed immediately after delivery (p less than 0.001). It has been known that adrenal secretion of corticosterone in response to exogenous ACTH occurs prior to that of cortisol. Consequently, our results suggest that the dramatic increase in the corticosterone serum concentration after delivery may be due to some physical stress in terms of labor pains, while the steady increase before labor must be due to physiological organic changes characteristic of pregnancy.