Risk of cerebral palsy in relation to pregnancy disorders and preterm birth: a national cohort study.

AIM: To assess the risk of developing cerebral palsy in relation to pregnancy disorders and preterm birth.

METHOD: By linking the Medical Birth Registry of Norway to other national registries, we identified all live births in Norway from 1967 through to 2001. Risks of cerebral palsy (CP) after preterm delivery and pregnancy disorders were estimated in different gestational age groups.

RESULT: In total, 1 764 509 children delivered at 23 to 43 weeks' gestation were included. The prevalence of CP was 1.8 per 1000 births. Absolute risk of CP was 8.5% among children born at 23 to 27 weeks' gestation, 5.6% at 28 to 30 weeks, 2.0% at 31 to 33 weeks, 0.4% at 34 to 36 weeks, and 0.1% thereafter. Placental abruption, chorioamnionitis, prolonged rupture of membranes, intrauterine growth restriction, pre-eclampsia, multiple births, placenta previa, bleeding, cervical conization, and congenital malformation were all associated with CP. Before 32 weeks' gestation, absolute risk of CP was highest with chorioamnionitis (9.1%) and lowest with pre-eclampsia (3.1%). Among those born after 31 weeks, the absolute risk of CP was more consistently (but also more slightly) increased with a recorded pregnancy disorder.

INTERPRETATION: Early delivery and pregnancy disorders were both strong risk factors for CP. The added risks with recorded pregnancy disorders varied within categories of gestational age.