Cerebral palsy risk rises in post term babies: Study

By Dr. Ananya Mandal, MDSep 2 2010

Babies born past their due dates – at 42 weeks or later, are at increased risk for cerebral palsy compared to those born at 40 weeks, according to new research. That said, the actual risk of cerebral palsy remains low. According to the CDC one in 303 children have some type of cerebral palsy. Common symptoms may include movement problems, muscle stiffness, poor muscle tone, and spasticity. The symptoms are thought to result from injury to the brain as a foetus or early in infancy.

The study was reported in the Sept. 1 issue of The Journal of the American Medical Association.

According to study researcher Dag Moster, of the University of Bergen, Norway, “The absolute risk is still very low, and the vast majority of children being born some weeks away from 40 weeks will not develop cerebral palsy… It would be hasty to recommend intervention on delivery time based on this study.” He also assured that “women having a normal delivery outside 40 weeks still have a very small risk that their child will develop cerebral palsy.”

For the study the team looked at 1,682,441 single births between gestational ages of 37 and 44 weeks with no birth defects in Norway from 1967 to 2001. Of these babies, 1,938 were diagnosed with cerebral palsy. The risk was higher at 37 and 38 weeks and at 42 weeks or later, compared with full-term, 40-week delivery, the study showed. The babies had to be followed up till 2005 to confirm the diagnosis since CP is not always evident at birth. Babies born at 37 weeks had about a 90% increased risk for cerebral palsy, compared to babies born at term. Compared to babies born at 40 weeks, babies born at 38 weeks had a 30% increased risk for cerebral palsy and those born at 42 weeks had about a 36% increased risk for cerebral palsy. This risk increased about 44% when babies were born after 42 weeks. These associations were stronger among babies whose gestational age was based on ultrasound measurements, which can be a more accurate way of dating a pregnancy.

According to Dr. Moster, “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… An alternative explanation may be that foetuses prone to develop cerebral palsy have a disturbance in timing of birth, making them more prone to be delivered either early or late.”

Amos Grunebaum, director of clinical maternal-foetal medicine at the New York Hospital-Cornell Weill Medical College in New York City also said, “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… More often than not, cerebral palsy diagnosis is due to events preceding labour and delivery… There are certain conditions where the fetus won't go into labour 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… Delivering more than two weeks after your due date does increase the risk for complications in general.”

Stephen Bennett, president and CEO of United Cerebral Palsy in Washington, D.C. said, “United Cerebral Palsy is looking forward to additional study about increased incidents of cerebral palsy in at term and post term births…Ongoing research about cerebral palsy and developmental disabilities is vital to helping to create a life without limits for people with disabilities. We applaud this ongoing research and hope that this study and others like it will continue to improve the lives of those with disabilities.”

Dr. Diane Ashton, deputy medical director of the March of Dimes said that “these findings are consistent with what we know about term gestation… Thirty-nine to 40 weeks tends to be the optimum time for delivery.” She explained, “There may be some insult that occurs earlier during the pregnancy and, probably, whatever that insult is disrupts the timing for birth and that might be one reason why you see cerebral palsy occurring according to gestational age.”