FRIDAY, Oct. 3, 2003 (HealthDayNews) -- Whatever causes cerebral palsy appears to happen primarily during pregnancy, not when a baby is delivered, a major European study indicates.
Records from 10 European registers listing 4,503 babies born with cerebral palsy show those with birth weights in the bottom 10 percent are four to six times more likely to have the condition than those in the normal range. The incidence was threefold higher for the babies with the very highest birth weight, says a report in the Oct. 4 issue of The Lancet.
Babies who are slightly above average weight have the lowest risk, the study finds.
"What this does is to add evidence suggesting that cerebral palsy, or the origin of cerebral palsy, occurs in utero," says study leader Dr. Mary-Jane Platt, a senior lecturer in public health at the University of Liverpool. "It adds to the body of evidence that cerebral palsy is not uniquely related to events at the time of birth."
Cerebral palsy is an overall name for a number of conditions in which brain damage affects the control of motion and that together are the most common cause of severe physical disability in children in developed countries.
It has long been believed that low birth weight is associated with an increased incidence of cerebral palsy, Platt says, but the observed link to very high birth weight is new.
The cause-and-effect relationship between birth weight and the risk of cerebral palsy is unclear, she says. The link to low birth weight "implies that something has impeded growth in utero," she says. "Whether impeded growth contributes to the risk of cerebral palsy or whether it is the cerebral palsy that impedes growth is not known. These are very different options, and there is no evidence in this paper to support either one."
The results are convincing because this is "the largest epidemiological study on cerebral palsy and birth weight, and it is unlikely that there will be similar studies in the future," says an accompanying editorial by Drs. Frederick B. Palmer and Mario C. Petersen of the University of Tennessee Boling Center for Developmental Disabilities.
"We know from other studies that cerebral palsy generally is not related to events at delivery," says Petersen, who is a professor of pediatrics at Tennessee. "While you cannot draw directly from this study that implication, you can say that since the risk is directly related to birth weight, it is not something that occurs at delivery."
And the finding that unusually high birth weight is a warning sign of cerebral palsy adds emphasis to something that obstetricians already are told to do: monitor the weight of the fetus throughout pregnancy, Petersen says.
An abnormal growth pattern can be a warning sign of a potentially treatable condition, such as an infection, and can signal "the need to prepare for (or prevent) mistimed delivery," the editorial says.
"What does seem certain is that these abnormal growth patterns indicate a process that commenced well before birth," the report says. "Increasingly, evidence is pointing to endocrine [hormonal] pathways, infection, coagulation defects, or even a 'vanishing twin' episode early in pregnancy as the primary cause in many cases of cerebral palsy."
The study results could help reduce the risk of cerebral palsy in some cases, Platt says. When a fetus is found to have abnormally low or high weight, special care during pregnancy and delivery is advisable to prevent or limit the damage that causes cerebral palsy.
Facts about cerebral palsy are available at the National Institute of Neurological Disorders and Stroke. Get tips on a healthy pregnancy from the March of Dimes.