Meta-analysis of the association between preterm delivery and intelligence

An increasing proportion of infants are born preterm, and their survival has improved. Therefore, their long-term sequelae are of increasing public health importance. We conducted a systematic review covering a 30 year period (19802009). A random effects meta-analysis provided a pooled estimate of the difference in IQ score between individuals born preterm and term. Small-study bias was examined using a funnel plot and Eggers test, and meta-regression was used to investigate possible causes of heterogeneity. Cumulative meta-analysis was used to determine if the magnitude of the association had changed over time. The 27 eligible studies covered 7044 individuals; 3504 (50) delivered preterm and 3540 (50) at term. They provided 37 estimates of difference in IQ. All demonstrated a reduced IQ among those delivered preterm and all but four reached statistical significance. Overall, IQ score was 11.94 (95 CI: 10.4713.42, P 0.001) points lower among children born preterm. There was moderate heterogeneity (overall I-2 74.2, P 0.001), but no significant small-study bias (P 0.524). The association between preterm delivery and IQ did not change significantly over time. There was a statistically significant, linear association across the gestational age range (adjusted coefficient: 0.91, 95 CI: 1.64, 0.17, P 0.018). There is a strong and consistent body of evidence suggesting an association between preterm delivery and reduced IQ, with evidence of a doseresponse relationship with gestational age.