Background: Childhood intelligence is an important determinant of health outcomes in adulthood. The first years\nof life are critical to child development. This study aimed to identify early life (perinatal and during the first year of\nlife) predictors of low cognitive performance at age 6.\nMethods: A birth cohort study started in the city of Pelotas, southern Brazil, in 2004 and children were followed from\nbirth to age six. Information on a broad set of biological and social predictors was collected. Cognitive abilityââ?¬â?the\nstudy outcomeââ?¬â?was assessed using the Wechsler Intelligence Scale for Children (WISC). IQ scores were standardized\ninto z-scores and low IQ defined as z < ?1. We applied bootstrapping methods for internal validation with a multivariate\nlogistic regression model and carried out external validation using a second study from the 1993 Pelotas Birth Cohort.\nResults: The proportion of children with IQ z-score < ?1 was 16.9% (95% CI 15.6ââ?¬â??18.1). The final model included the\nfollowing early life variables: childââ?¬â?¢s gender; parentsââ?¬â?¢ skin color; number of siblings; fatherââ?¬â?¢s and motherââ?¬â?¢s employment\nstatus; household income; maternal education; number of persons per room; duration of breastfeeding; height-for-age\ndeficit; head circumference-for-age deficit; parental smoking during pregnancy; and maternal perception of the childââ?¬â?¢s\nhealth status. The area under the ROC curve for our final model was 0.8, with sensitivity of 72% and specificity of 74%.\nSimilar results were found when testing external validation by using data from the 1993 Pelotas Birth Cohort.\nConclusions: The study results suggest that a childââ?¬â?¢s and her/his familyââ?¬â?¢s social conditions are strong predictors of\ncognitive ability in childhood. Interventions for promoting a healthy early childhood development are needed\ntargeting children at risk of low IQ so that they can reach their full cognitive potential.
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