Maternal smoking during pregnancy and intelligence quotient in offspring: a systematic review and meta-analysis

Abstract Background Exposure to tobacco during pregnancy may disrupt fetal brain development and impact offspring cognitive development. Aims To perform a systematic review and meta-analysis on maternal smoking during pregnancy and intelligence quotient (IQ) in childhood, adolescence, and adulthood. Methods We searched PubMed, Lilacs, PsycINFO, and Web of Science. Original articles evaluating tobacco use/exposure during pregnancy and the offspring’s IQ as the outcome. The review protocol is registered in PROSPERO (number CRD 42019116257). For the meta-analysis, we included studies with information on the regression coefficient and its confidence interval (CI) or standard error. Random effects model was used for pooling the estimates. Results 25 studies were included in the review, and of these 14 met the inclusion criteria for the meta-analysis. The overall pooled estimate showed that subjects who were exposed to maternal smoking during pregnancy presented lower IQ scores, compared to those not exposed to maternal smoking (β -1.30; 95% CI ―1.74, ―0.86; I2 = 87.8%); IQ scores were also lower in crude (β -5.46; 95% CI -7.31, -3.60; I²: 79.0%) and adjusted pooled estimates (β =―0.45; 95% CI ―0.76, ―0.13; I2 = 80.4%), for the group exposed to maternal smoking. In the stratified analysis, an inverse association was also observed in studies with large sample size (n≥1000 participants) (β=―0.49; 95% CI ―0.96, ―0.02), among those performed with adolescents (β=―1.16; 95% CI ―2.18, ―0.14), and among those adjusted for maternal education (β=―0.57; 95% CI ―1.05, ―0.08). Conclusions Our findings suggest that exposure to tobacco during pregnancy may have negative effects on IQ. However, the findings of this meta-analysis should be interpreted with caution.