Birth before or after 40 weeks raises cerebral palsy risk

Infants delivered at 37 or 38 weeks' gestation or at 42 weeks or later are at increased risk for cerebral palsy compared with those delivered at 40 weeks, according to the findings of a recent study from Norway.

Researchers analyzed data from a national birth registry and the national health insurance system on more than 1.6 million singleton children born without congenital anomalies between 1967 and 2001 at a gestational age of 37 through 44 weeks. Of the cohort, 1,938 had cerebral palsy.

The lowest risk for cerebral palsy was found in infants born at 40 weeks (prevalence of 0.99 per 1,000; 95% CI, 0.90-1.08). Prevalence at 37 weeks was 1.91 per 1,000 (95% CI, 1.58-2.25) with a relative risk (RR) of 1.9 (95% CI, 1.6-2.4) and at 38 weeks was 1.25 per 1,000 (95% CI, 1.07-1.42) with a RR of 1.3 (95% CI, 1.1-1.6). Prevalence at 42 weeks was 1.36 per 1,000 (95% CI, 1.19-1.53) with a RR of 1.4 (95% CI, 1.2-1.6) and after 42 weeks was 1.44 per 1,000 (95% CI, 1.15-1.72) with a RR of 1.4 (95% CI, 1.1-1.8).