Objective: To identify perinatal factors associated with cerebral palsy (CP).
Methods: This was a case-control study based on the Swedish Medical Birth Registry and the Swedish Hospital Discharge Registry, including 2,303 infants born in Sweden 1984-1998 with a diagnosis of CP and 1.6 million infants without this diagnosis. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.
Results: Infants born preterm had a highly increased risk for CP, and constituted 35% of all cases; OR 34 (95% CI 29-39) in weeks 23-27, OR 37 (95% CI 32-42) in weeks 28-29, OR 26 (95% CI 23-30) in weeks 30-31, and OR 3.9 (95% CI 3.4-4.4) in weeks 32-36. Boys had a higher risk (sex ratio 1.36:1), particularly before term (sex ratio 1.55:1). Other factors associated with CP were being small or large for gestational age at birth, abruptio placentae (OR 8.6, 95% CI 5.6-13.3), maternal insulin-dependent diabetes mellitus type 1 (OR 2.1, 95% CI 1.4-3.1), preeclampsia (OR 1.5, 95% CI 1.3-2.4), being a twin (OR 1.4, 95% CI 1.1-1.6), maternal age older than 40 years (OR 1.4, 95% CI 1.1-1.8) or 35-39 years (OR 1.2, 95% CI 1.1-1.4), primiparity (OR 1.2, 95% CI 1.1-1.3), and smoking (OR 1.2, 95% CI 1.1-1.3). In term infants, low Apgar scores were associated with a high risk for CP; OR 62 (95% CI 52-74) at score 6 at 5 minutes, OR 498 (95% CI 458-542) at score 3. Other factors associated with CP in term infants were breech presentation at vaginal birth (OR 3.0, 95% CI 2.4-3.7), instrumental delivery (OR 1.9, 95% CI 1.6-2.3), and emergency cesarean delivery (OR 1.8, 95% CI 1.6-2.0).
Conclusion: Preterm birth entails a high risk for CP, but 65% of these children are born at term. Several obstetric factors and low Apgar scores are associated with CP.
Level of evidence: II-2.