Results of an epidemiologic study of postdate pregnancy.

Obstetric and neonatal data on 18,610 deliveries between 1975 and 1982 were analyzed to determine the risks associated with postdate pregnancy in an era of routine fetal heart rate monitoring. Thirteen percent of the deliveries occurred between 42 and 43 weeks' gestation, and 1% occurred at 44 weeks or later. There was a nonsignificant rise in the perinatal mortality rates for 38-41-week deliveries as compared to those delivered at 42 weeks or later. However, the perinatal mortality rate was six times higher for small-for-gestational-age infants. There was a significant rise in the perinatal morbidity in infants delivered at or beyond 42 weeks (5% incidence). This finding implies that the sensitivity of currently used screening tests for perinatal mortality is good but that it is unsatisfactory for the detection and prevention of morbidity.