Babies born prematurely or later than term could be at a slightly greater risk of developing cerebral palsy, says a new study conducted by researchers in Norway.

While earlier studies have suggested a direct association between cerebral palsy and preterm birth, the latest research is the first to link the neurological condition with delayed birth, though the researchers admit that the risk is still very small.

The study, published in the Journal of the American Medical Association, quotes lead researcher Dr. Dag Moster at the University of Bergen as saying that though there wa a statistical difference in the relative risk, it was important to underscore the fact that the absolute risk is still very low among children born some weeks after the 40-week pregnancy.

Dr. Moster also suggests that it could be hasty to recommend intervention on delivery time based on this study because women having a normal delivery outside 40 weeks still face a very small risk that their child will develop cerebral palsy.

The researchers looked at the risk of cerebral palsy among 1.6 million children born between 1967 and 2001 between weeks 37 to 44 of the pregnancy with no stated birth defects. Thereafter, the team tracked the children through 2005 by linking the data from the Medical Birth Registry of Norway to other national data banks.

It was found that among those born past-term, 1,938 patients developed cerebral palsy, while infants born at 40 weeks had the lowest risk of the disease. Those born at 37 weeks had a 90 percent higher risk of cerebral palsy, while at 38 weeks the risk dropped to 30 percent. But, it rose again to 40 percent at 42 weeks and later, the study says.

The researchers further suggested that factors like the baby's sex, the mother's age and socioeconomic factors did not seem to have any effect on these associations, though they admitted that till date the biological mechanisms underlying them were unclear.

Dr. Moster indicated that a possible explanation could be the neonatal brain being more vulnerable when the baby is born away from the gestational age of 40 weeks. It could also be a case of the fetus undergoing a disturbance during birth that results in the development of cerebral palsy at a later stage.

Medical experts believe that the findings of the latest research were consistent with available information on delivery with the best period between week numbers 39 and 40 of the gestation. It was felt that more research needs to be done on the past-term births as the available data was too small to assess the impact.