Cerebral palsy in children born after in vitro fertilization. Is the risk decreasing?

BACKGROUND: Infants born after in vitro fertilization (IVF) differ from spontaneously conceived infants in a number of aspects which could increase the risk for future cerebral palsy (CP), e.g., multiple births, preterm births, neonatal complications. AIMS: To follow up children conceived by IVF with respect to risk for CP. METHODS: Infants born after IVF were identified from all IVF clinics in Sweden 1982-2007. Perinatal characteristics were obtained by linkage with the Medical Birth Register. The presence of CP in children born after IVF and in other children was identified from the Patient Register which contains diagnoses given at hospitalizations or specialist outpatient clinics. The risk for CP after IVF was studied after adjustment for year of birth, maternal age, parity, and smoking, all factors which co-vary both with IVF and with CP. Stratification was made for singletons and multiple births and for various neonatal outcomes. RESULTS: The adjusted odds ratio for CP after IVF was 1.81 (95% confidence interval, 95% CI 1.52-2.13), lower and not statistically significant when singletons or when unlike-sexed twins were analyzed. Stratification for various neonatal characteristics also reduced odds ratios to non-significant levels. For the last few years of the study (2004-2007) when the twinning rate after IVF was <10%, the odds ratio for CP was 0.97 (95% CI 0.57-1.66). CONCLUSIONS: The moderately increased risk for CP was most likely a consequence of an increased risk of neonatal morbidity, notably associated with multiple births.