While preterm birth is a known risk factor for cerebral palsy (CP), a population-based study conducted by researchers at the University of Bergen, Norway, found that compared with delivery at 40 weeks, birth at 37 or 38 weeks gestation, or at 42 weeks or later, is also associated with an increased risk of CP. The results of the study were published in the September 1 issue of the Journal of the American Medical Association (JAMA).
Dag Moster, MD, PhD, and colleagues, examined the Medical Birth Registry of Norway between the years 1967-2001 and considered the relation of CP risk with gestational age in infants between 37 and 44 weeks with no congenital anomalies. Of the 1,682,441 children in the study, 1,938 were identified as having CP.
“One of the strongest predictors of CP is preterm birth, with the risk of CP increasing steadily with earlier delivery,” the authors write. “Although the risk is lower among term births, about three-fourths of all infants with CP are born after 36 weeks. Within this range of term births, there are few data on the possible association of CP with gestational age.”
They continue, “Clinicians typically regard term births (37-41 weeks) as low risk, with the possibility of increased risk with post-term delivery. This standard definition of term does not correspond well with the period of lowest risk for CP in this study or with the weeks when most infants are born.” The researchers claim that 39 to 41 weeks is the optimum time for delivery and conclude, “intervention at 40 weeks might reduce CP risk, while elective delivery at 37 or 38 weeks might increase it.” They temper this conclusion, however, by adding, “it would be hasty to assume that interventions on gestational age at delivery could reduce the occurrence of CP.”