Maternal plasma adrenocorticotropin and cortisol relationships throughout human pregnancy.
Adrenocorticotropin (ACTH) and cortisol in plasma were measured weekly from early in gestation through delivery in five women whose pregnancies were normal. During the twelfth week of pregnancy, the concentration of ACTH in plasma of blood samples obtained between 0800 and 0900 hours was 23 +/- 4.6 pg/ml (mean and SEM) and rose progressively to 59 +/- 16 pg/ml at 37 weeks. The levels of ACTH in plasma were significantly lower throughout pregnancy than those found in nonpregnant women. During labor and delivery, ACTH levels rose strikingly to values of 301 +/- 137 pg/ml. As pregnancy advanced, the concentration of cortisol in plasma increased progressively from 149 +/- 34 ng/ml (mean and SEM) at 12 weeks to 352 +/- 90 ng/ml at 26 weeks' gestation but changed minimally thereafter until labor commenced, during which values of 706 +/- 148 ng/ml were achieved. ACTH and cortisol secretory patterns over a 24-hour period were also investigated in one subject during each trimester of pregnancy. Diurnal variations were observed that were qualitatively similar to those seen in nonpregnant women. From the results of these studies, we conclude that ACTH levels are suppressed in plasma of normal pregnant women but are higher in late pregnancy than in early pregnancy. The rise in plasma ACTH concentrations, as pregnancy advances, in spite of increasing levels of plasma cortisol, estrogens, and progesterone, is suggestive of the possibility that a source of ACTH exists that is not subject to negative feedback control, that the clearance of free cortisol increases as pregnancy advances, or that there is an alteration in the metabolism of the ACTH precursor protein produced by the pituitary and/or placenta.