Residential air pollution and infant mental development country of origin, or number of siblings at birth [see Supplemental Material, Table 3 (http://dx.doi.org/10.1289/ehp.1103469)]. However, children not included had lower parental social class, lower maternal educa- tion, higher maternal smoking use, higher proportion of one-parent families, younger mothers, lower gestational age, lower birth weight, higher proportion of boys, and shorter breast-feeding duration. Among the 1,889 children included in the analysis, mean air pollution exposure during pregnancy was 29.0 μg/m 3 (range, 20.1–36.8 across regions) for NO2 and 1.5 μg/m 3 (range, 0.8–2.3) for benzene (Table 1). Exposure to NO2 and benzene was inversely associated with mental development, although relationships were not statistically significant, in unadjusted models and after adjusting for a large array of potential con- founders (Figure 1). Among regions, main effect estimates were significant for Gipuzkoa only [β (95% CI) = –5.15 (–8.04, –2.27) and –5.49 (–9.21, –1.76), respectively, for a dou- bling of each compound]. When we stratified by antioxidant and detoxification variables, we found a strong and significant inverse relationship between NO2 and benzene and mental development score among infants with low maternal intakes of fruits and vegetables during the first tri- mester of pregnancy, but little evidence of an association among infants whose mothers had higher intakes (interaction p-values = 0.073 and 0.047, respectively) (Table 2). Inverse associations with NO2 and benzene were also stronger in infants that were not breast-fed and for infants whose mothers had low cir- culating vitamin D during pregnancy than in other infants, although stratum-specific estimates and interactions were not significant (Table 2). Associations between air pollution and infant mental development were not sig- nificantly different according to parental social class or education level (p > 0.20) (Table 2). Region-specific effect estimates were rela- tively homogeneous for infants whose mothers had low fruit and vegetable intakes (heteroge- neity p-values of 0.3 and 0.7 for associations with NO2 and benzene, respectively) compared with the high-intake group (heterogeneity Effect per doubling in NO2 levels during pregnancy Forest plot Effect per doubling in benzene levels during pregnancy Forest plot Region Valencia (n = 608) Sabadell (n = 471) Asturias (n = 345) Gipuzkoa (n = 465) Combined (n = 1,889) β coefﬁcient (95% CI) –0.43 (–2.86, 2.01) 1.98 (–1.69, 5.66) 0.17 (–2.71, 3.04) –5.15 (–8.04, –2.27) –0.95 (–3.90, 1.89) Region Valencia (n = 608) Sabadell (n = 471) Asturias (n = 312) Gipuzkoa (n = 463) Combined (n = 1,854) Each cell represents a random-effect model by region from a meta-analysis. aAdjusted for psychologist, child’s sex, child’s age at mental development assessment, maternal education, maternal age, maternal height and prepregnancy body mass index, mater- nal alcohol use during pregnancy, maternal large fatty and lean fish consumption at first trimester, season-specific maternal circulating vitamin D level at pregnancy, use of gas stove at home during pregnancy, and number of siblings at birth. bp-Values for interaction terms based on region-specific interactions that were combined using meta-analysis. cLow versus medium/high tertile of maternal fruit and vegetable consumption. dSeason-specific tertiles of maternal circulating vitamin D levels (see “Materials and Methods”). These models were not adjusted for maternal vitamin D levels at pregnancy. eSocial class data from Instituto Nacional de Estadística (1994). Environmental Health Perspectives • volume 120 | number 1 | January 2012 β coefﬁcient (95% CI) –1.83 (–4.72, 1.06) 0.67 (–2.17, 3.51) –0.81 (–2.74, 1.13) –5.49 (–9.21, –1.76) –1.57 (–3.69, 0.56) p-Valueb interaction 0.047 0.133 0.070 0.292 0.241 0.727 0.614 0.665 0.797 147 –10 –8 –6 –4 –2 0 2 4 6 –10 –8 –6 –4 –2 0 2 4 6 Figure 1. Region and summary risk estimates (β-coefficient and 95% CI) for a doubling in NO2 levels (A) and benzene levels (B) during pregnancy and infant men- tal development, adjusted for psychologist, child’s sex, child’s age at mental development assessment, maternal education, maternal age, maternal height and prepregnancy body mass index, maternal alcohol use during pregnancy, maternal large fatty and lean fish consumption at first trimester, season-specific mater- nal circulating vitamin D level at pregnancy, use of gas stove at home during pregnancy, and number of siblings at birth. (A) Test for heterogeneity: Q = 11.314 on three degrees of freedom (p = 0.010). (B) Test for heterogeneity: Q = 7.084 on three degrees of freedom (p = 0.068). The size of the markers for each β-coefficient represents the relative weight that each region contributed to the summary regression slope. Table 2. Adjusted association for a doubling in NO2 and benzene levels during pregnancy and infant mental development.a Effect per doubling in NO2 levels during pregnancy Effect per doubling in benzene levels during pregnancy Characteristics Maternal fruit and vegetable consumption, first trimesterc Low tertile (≤ 405 g/day) Medium/high tertile (> 405 g/day) Breast-feeding duration None < 6 months ≥ 6 months Maternal circulating vitamin D levelsd Low Medium High Parental social classe I/II managers/technicians III skilled manual/nonmanual IV/V semiskilled/unskilled Maternal education level Primary or less Secondary University degree n 627 1,249 270 745 826 607 597 605 619 486 783 429 776 679 β-Coefficient (95% CI) –4.13 (–7.06, –1.21) 0.25 (–3.63, 4.12) –3.47 (–7.82, 0.98) –0.71 (–4.06, 2.65) –0.61 (–2.97, 1.75) –2.49 (–6.87, 1.89) –0.55 (–3.48, 2.39) –0.11 (–2.72, 2.49) –1.02 (–5.23, 3.19) 0.16 (–3.79, 4.11) –1.57 (–3.76, 0.62) –0.90 (–6.54, 4.73) –2.22 (–5.13, 0.70) –0.72 (–3.93, 2.49) p-Valueb interaction 0.073 0.274 0.196 0.571 0.268 0.565 0.725 0.795 0.630 n 613 1,228 262 729 816 594 586 597 605 476 772 425 765 659 β-Coefficient (95% CI) –4.37 (–6.89, –1.86) –0.60 (–3.66, 2.46) –3.53 (–7.15, 0.08) –2.42 (–6.08, 1.25) 0.05 (–2.22, 2.31) –2.34 (–5.34, 0.04) –0.26 (–2.87, 2.38) –0.34 (–3.17, 1.75) –1.00 (–3.32, 1.32) –0.62 (–3.55, 2.32) –2.25 (–5.19, 0.68) –2.58 (–7.56, 2.41) –1.46 (–4.95, 2.03) –1.22 (–3.45, 1.01)