Possible role of the fetal adrenal glands in the etiology of postmaturity.

Plasma cortisol levels were studied in the cord blood and neonatal blood of the following vaginally delivered groups: (A) postmature; (B) postterm (but not postmature); and (C) term neonates. Significantly lower levels of 8 A.M. neonatal plama cortisol were found in postmature neonates when compared with term neonates (P LESS THAN 0.02) or merely postterm neonates (P LESS THAN 0.02). No difference was found in the cord blood cortisol levels in all three groups. Contrary to the traditional belief that postmaturity results from placental aging, our findings appear to indicate that postmaturity represents a specific fetal disorder. Fetal adrenal insufficiency may be a characteristic of this disorder. Prolonged pregnancy in these cases may be reflected inability of the affected fetus to initiate labor.