Resuscitation at Birth and Cognition at 8 Years of Age: A Cohort Study

Abstract

Severe hypoxic injury causing encephalopathy during the neonatal period is associated with impaired cognitive function in later life. It is unclear whether mild degrees of hypoxia that do not cause encephalopathy during the neonatal period can result in reduced intelligence quotient (IQ) scores in childhood. The aim of this cohort study was to determine whether infants who received resuscitation after birth, but had no symptoms of encephalopathy have reduced IQ scores in childhood. IQ scores in 3 groups of children at mean age of 8.6 years (SD 0.33) were measured. The groups included neonates asymptomatic for encephalopathy who needed resuscitation but had no further care (n = 815), neonates symptomatic for encephalopathy who were resuscitated and required neonatal care (n = 58), and healthy infants asymptomatic for encephalopathy who were not resuscitated, and had no further neonatal care (n = 10,609). An IQ score below 80 was defined as a low IQ. A shortened version of the Weschler intelligence scale for children (WISC-III) provided full-scale IQ data for 5887 children but only 4857 of these had complete data on resuscitation status, IQ data, and covariables. There was no data for 5529 children in the cohort. To reduce selection bias, the chained equations missing data method was used to impute missing confounder values in the 5529 nonresponders. Data were adjusted for clinical and socioeconomic potential confounders. In the final logistic regression model, infants without symptoms of encephalopathy in the neonatal period who required resuscitation were at increased risk of a low full-scale IQ score (adjusted odds ratio, 1.65; 95% confidence interval [CI], 1.13–2.43, P < 0.010). The risk of a low IQ among resuscitated infants who developed encephalopathy was almost 4 times greater (adjusted odds ratio, 6.22; 95% CI, 1.57–24.65, P < 0.009). Because the total number of resuscitated infants asymptomatic for encephalopathy was 14 times greater than that of infants with encephalopathy, the proportion of infants with low IQ scores that might be attributable to the need for resuscitation at birth was higher for asymptomatic infants (3.4%, with a 95% CI of 0.5–6.3) compared with symptomatic infants (1.2%, with a 95% of 0.2–2.2). These findings suggest that mild hypoxia or other perinatal events at birth may cause subtle brain damage that increases the risk for low IQ in childhood. Because of differences in population size, resuscitated infants without encephalopathy may account for a larger proportion of children and potentially adults with low IQ scores than that attributable to infants who develop encephalopathy.