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

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 42,019,116,257). 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 (13 -1.30; 95 % CI -1.74, -0.86; I2 = 87.8 %); IQ scores were also lower in crude (13 -5.46; 95 % CI -7.31, -3.60; I2: 79.0 %) and adjusted pooled estimates (13 =-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) (13=-0.49; 95 % CI -0.96, -0.02), among those performed with adolescents (13=-1.16; 95 % CI -2.18, -0.14), and among those adjusted for maternal education (13=-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.