Delayed childbearing and the outcome of pregnancy.

Whether women who delay childbearing are at increased risk for adverse outcomes of pregnancy is of concern because of the growing proportion of first births to older women. We assessed the effect of advancing maternal age on the outcome of pregnancy in first births in a hospital-based cohort study of 3917 private patients who were 20 years of age or older with a singleton gestation. There was a slight elevation in the risk of having a low-birth-weight infant among women who were 35 years of age or older (adjusted odds ratio, 1.3; 95 percent confidence interval, 0.9 to 1.9) as compared with the risk among women 20 to 29 years of age. However, there was no evidence that women between 30 and 34 or those 35 and older had an increased risk of having a preterm delivery or of having an infant who was small for gestational age, had a low Apgar score, or died in the perinatal period. In contrast, even after controlling for sociodemographic and medical risk factors, we found that women who were 35 or older were significantly more likely to have specific antepartum and intrapartum complications and those who were 30 or older were significantly more likely to have both cesarean sections and infants who were admitted to the newborn intensive care unit. This study suggests that although older primiparous women have higher rates of complications of pregnancy and delivery, their risk of a poor neonatal outcome is not appreciably increased.