Pregnancies extending more than 3 weeks beyond the expected date of confinement were studied among 9,719 single, white births from the Child Health and Development Studies in Oakland, California, and 358,702 births representing all white, singleton pregnancies in New York City terminating from 1957 through 1959.
The incidence of prolonged pregnancy was 7.3% in the Child Health and Development Studies and 5.4% in New York City. Younger women, primigravidas, and women of high parity showed an increased incidence.
Fetal and neonatal mortality rates were approximately doubled in prolonged pregnancy in both Oakland and New York City. This relationship held for both primiparas and multiparas, for antepartum and intrapartum fetal deaths, and for all major causes of fetal and neonatal mortality.
Post-term infants weighing less than 2,500 gm (5½lb) had a neonatal mortality rate seven times the rate for prolonged pregnancies as a whole. There was no increase in neonatal mortality among post-term infants weighing more than 4,100 gm (9 lb) compared with prolonged pregnancy infants between 2,500 and 4,100 gm (5½ to 9 lb).
There was a slightly increased incidence of congenital anomalies in the prolonged gestation group. Neonatal mortality in infants with severe congenital anomalies was substantially higher in prolonged pregnancy.
The excess mortality experience of prolonged pregnancy children continued for at least the first 2 years of life. Hospitalization and clinic visit data also implied a poorer health status in these children over the first 3 years of life.
Data on growth and intelligence revealed no difference between children with prolonged and normal gestation in a small group examined at age 5.
There were no gross placental findings to support the hypothesis of placental senility as a cause of pathology in prolonged pregnancies.
A tendency was noted for prolonged pregnancy to recur in successive gestations.
Maternal Smoking, Alcohol Consumption, and Caffeine Consumption during Pregnancy in Relation to a Son's Risk of Persistent Cryptorchidism: A Prospective Study in the Child Health and Development Studies Cohort, 1959–1967