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Timing of Delivery May Affect Cerebral Palsy Risk

Study Shows Risk May Be Higher for Babies Born at 37 or 38 Weeks -- or 42 Weeks or Later

Cerebral Palsy Risk continued...

Exactly what causes cerebral palsy is unknown, but risk is known to increase with complicated labor and delivery, including preterm delivery, which was reinforced in this study.

As to why post-term delivery may increase the risk of cerebral palsy, "one possible explanation may be that the neonatal brain is especially vulnerable the more the baby is born away from a gestational age of 40 weeks," speculates Moster. "An alternative explanation may be that fetuses prone to develop cerebral palsy have a disturbance in timing of birth, making them more prone to be delivered either early or late."

Second Opinion

Amos Grunebaum, MD, director of clinical maternal-fetal medicine at the New York Hospital-Cornell Weill Medical College in New York City, stresses that the risk of cerebral palsy is very low to begin with. "There is only a small risk of one in 1,000 births to begin with, and there are many different possible causes of cerebral palsy," he says.

"More often than not, cerebral palsy diagnosis is due to events preceding labor and delivery," he says. "There are certain conditions where the fetus won't go into labor naturally, and the women in the study who delivered after 42 weeks may have already had a baby with CP."

"Delivering a baby earlier doesn't prevent it, but certainly you don't want to deliver a baby after 42 weeks and not before 39 unless there are medical reasons for doing so," he says. "Delivering more than two weeks after your due date does increase the risk for complications in general."

"It's hard to know whether these relationships are causal or just reflect a biology in motion," says Dwight Rouse, MD, professor of obstetrics and gynecology at the Alpert School of Medicine at Brown University in Providence, R.I., and an attending physician in the department of maternal and fetal medicine at Women and Infant's Hospital of Rhode Island.

"Babies destined to be abnormal often don't deliver when they are supposed to," he tells WebMD. "The relatively higher risk at 37 and 38 weeks as opposed to 39 or 40 weeks may be one reason to avoid elective early delivery, [but] if there is a good reason to deliver at 37 weeks, this study should not alter that," he says.

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