Further observations on adrenal cortical function during pregnancy

1.1. Free plasma hydrocortisone levels are increased in the third trimester of pregnancy.2.2. There is an apparent exaggeration of free plasma 17-OH-corticosteroid response to ACTH in the third trimester which disappears by the end of the first week post partum. The excessive response may be partly accounted for by a delay in the clearance of hydrocortisone from plasma in late pregnancy.3.3. Free urinary corticoid values are increased in late pregnancy, but the response to ACTH of total urinary corticoids (free plus glucuronides) is no greater than normal.4.4. The hypothesis is advanced that there may be in late pregnancy a resistance to the effects of hydrocortisone upon various tissues (e.g., the anterior pituitary), perhaps because some physical factor, as yet unknown, renders a portion of the circulating corticosteroid biologically inert.