UC Irvine

The purpose of this study was to examine whether postterm gestational age increases the risk of neonatal mortality.

We retrieved data from 1,815,811 liveborn infants in California from 1999 to 2003. We excluded multiple births and congenital anomalies, as well as infants with a gestational age of less than 38 w0d, or greater than 42 w6d, weeks. We used multivariable logistic regression models to adjust for demographic variables thought to confound the association.

Compared to infants born at 38, 39, or 40 weeks, those born at 41 w0d to 42 w6d have a greater odds of neonatal mortality (aOR: 1.34, 95% CI, 1.08-1.65). Subdividing by gestational week, infants delivered at 41 w0d to 41 w6d showed elevated mortality relative to earlier term births (aOR: 1.37, 95% CI, 1.08-1.73). Additional analyses support this increased neonatal mortality across all normal birthweight categories.

Infants born beyond 41 w0d of gestation experience greater neonatal mortality relative to term infants born between 38 w0d and 40 w6d.