Preterm birth is a known risk factor for cerebral palsy, but researchers have now added weeks 37 and 42+ to that list. According to a study published by the Journal of American Medical Association, the lowest risk occurs when children are born at 40 weeks.

Gauging gestational ages and pregnancy week is a nearly exact science with fetal ultrasound and blood testing. However, nearly may not be good enough. About 1.91 of every 1,000 infants born at 37 weeks gestation are diagnosed with cerebral palsy. This is a 90% increased over normal rates of 1 per 0.99 per 1,000. At 42 weeks gestation, the rate is 1.36 per 1,000 births and after 42 weeks the number goes up to 1.44 per 1,000. Researchers agree the optimal gestational age for delivery is 39 to 41 weeks.

The study reviewed patient records taken between 1967 and 2001. A total of 1,682,441 infant patient records were evaluated for cerebral palsy diagnosis and gestational age at birth. If a planned delivery is desired or required, obstetricians should try to aim for weeks 39 to 41. Children who are at risk for cerebral palsy due to genetic factors do not appear to be at higher risk with early or late delivery.

No mention of multiple pregnancies or multiple births were made in the article. Multiples are typically born early due to increased uterus size and weight.

Source: Dag Moster MD, Ph.D., Allen J. Wilcox MD, Ph.D., Stein Emil Vollset MD, DrPH, Trond Markestad MD, Ph.D., Rolv Terje Lie Ph.D. Journal of the American Medical Association. 1 September 2010.