Assessment of fetal risk in postdate pregnancies.

To assess postdate fetal risk, pregnancies in which menstrual history was confirmed by early ultrasound examination were reviewed; 5915 pregnancies within 1 week of term, 1408 1 to 2 weeks postdate, and 340 at least 2 weeks postdate. Fetal distress and meconium release were twice as frequent and meconium aspiration eight times as frequent postterm. Birth asphyxia was unrelated to gestational age. Fractures and palsies were more frequent because of primiparity and macrosomia. Only one antepartum fetal death occurred in 1748 postdate pregnancies. Review of 674 perinatal deaths at 37 plus weeks in Quebec showed no increase in deaths postterm. The increase in fetal distress and meconium aspiration postterm without an increase in birth asphyxia or fetal death may reflect greater responsiveness of the more mature fetus to mild asphyxic insults. Findings of this study could not justify increased fetal monitoring in postdate pregnancies.