Background: Cerebral palsy seems to be more common in term babies whose birthweight is low for their gestational age at delivery, but past analyses have been hampered by small datasets and Z-score calculation methods.
Methods: We compared data from ten European registers for 4503 singleton children with cerebral palsy born between 1976 and 1990 with the number of births in each study population. Weight and gestation of these children were compared with reference standards for the normal spread of gestation and weight-for-gestational age at birth.
Findings: Babies of 32-42 weeks' gestation with a birthweight for gestational age below the 10th percentile (using fetal growth standards) were 4-6 times more likely to have cerebral palsy than were children in a reference band between the 25th and 75th percentiles. In children with a weight above the 97th percentile, the increased risk was smaller (from 1.6 to 3.1), but still significant. Those with a birthweight about 1 SD above average always had the lowest risk of cerebral palsy. A similar pattern was seen in those with unilateral or bilateral spasticity, as in those with a dyskinetic or ataxic disability. In babies of less than 32 weeks' gestation, the relation between weight and risk was less clear.
Interpretation: The risk of cerebral palsy, like the risk of perinatal death, is lowest in babies who are of above average weight-for-gestation at birth, but risk rises when weight is well above normal as well as when it is well below normal. Whether deviant growth is the cause or a consequence of the disability remains to be determined.