Maternal body weight and pregnancy outcome.

Pregnancies that produced 56,857 children were analyzed to evaluate the relationship of the mothers' relative pregravid body weight to pregnancy outcome. Perinatal mortality rates progressively increased from 37 of 1000 in offspring of thin subjects to 121 of 1000 in the offspring of obese subjects (p less than 0.001). Nearly half of this mortality increase was due to preterm deliveries, particularly before 31 wk of gestation. More than half of the increase in preterm births was caused by acute chorioamnionitis. Other factors that made major contributions to the overall mortality increase were rises in the frequencies of older gravidas (ages 35-50 y), gravidas who had diabetes mellitus, children who had major congenital malformations, and dizygous twins.