Aims: Although research on fetal alcohol exposure has had a significant effect on social norms and public policy, there has been little quantitative review of this literature. Methods: Meta-analysis was used to examine the effects of prenatal alcohol exposure on infant mental development, assessed using the Mental Development Index (MDI) from the Bayley Scales of Infant Development, a widely used, standardized measure. The current study examined the effects of three levels of average daily exposure during pregnancy: less than 1 drink per day, 1-1.99 drinks per day and 2 or more drinks per day. Analyses were conducted separately for effects derived from observations of 6-8-, 12-13- and 18-26-month-old children. Results: Fetal alcohol exposure at all three dosage levels was associated with significantly lower MDI scores among 12-13-month-olds. The effect was attenuated, but not eliminated, when effect sizes adjusted for relevant covariates were used. For younger and older children, the effect of fetal alcohol exposure did not attain statistical significance at any dosage level. Conclusions: This pattern of results may reflect differences in MDI item content at different ages and the differential sensitivity of these abilities to prenatal alcohol exposure. Because the body of relevant literature is neither large nor conclusive, and because of heterogeneity in measurement, analysis and samples, caution is urged in interpreting results. Future research would benefit from use of more specific measures of infant outcomes and consideration of the impact of relevant covariates, different dosage patterns and timing of drinking on infant mental development.
