Aguilera et al. restrict our analysis to two subsets: a) women maternal height and prepregnancy weight, statistically significant for all the activities. who spent more time at home and b) women and paternal height and weight. During weekdays, women who did not work who spent less time in nonresidential outdoor We examined whether air pollution expo- during pregnancy or worked only during part environments. Because we based LUR esti- sure was associated with maternal education of it (n = 350) spent more time at home and mates on the women’s residential addresses, as a surrogate of socioeconomic status (SES). in nonresidential outdoor environments, and we assumed that these two subsets suffered We found a small but statistically significant less time in means of transportation, com- less from exposure misclassification and that association between LUR estimates of BTEX pared with women who worked during the misclassification was nondifferential. levels and maternal education (p = 0.02). entire pregnancy (n = 210) (Mann–Whitney We performed statistical analyses using Predicted annual mean levels of BTEX were test, p < 0.05). We found no differences in 17.6, 16.0, and 16.1 µg/m3 for women with Stata 8.2 (StataCorp., College Station, TX, total time spent in indoor environments USA). a university degree, secondary education, and between the two groups. primary education, respectively. The corre- Table 5 presents the effect of air pollution Results sponding NO2 values for the three categories exposure during pregnancy and during each were 37.4, 35.7, and 35.7 µg/m3 (p = 0.14). Mean birth weight of included births was trimester on birth weight. Neither NO2 nor 3,247 g (10th, 50th, and 90th percentiles: Tables 2 and 3 provide the distribution of BTEX exposure was significantly associated 2,721, 3,288, and 3,760 g), and mean 9-month and trimester-specific exposures to with the outcome in any of the exposure peri- maternal age was 31.4 years (minimum and NO2 and BTEX and the correlation coefficients ods. Associations for BTEX were more pro- maximum, 18.2 and 43 years, respectively). among them, respectively. We found only slight nounced in the subset of women who spent Table 1 shows other characteristics of the differences between mean exposure levels by tri- ≥ 15 hr/day at home (n = 276), but they were study population and mean birth weight for mester and 9-month exposures, although the also not statistically significant. However, each categorized variable. Birth weight was range of exposure was wider for the three tri- when considering only women who spent associated (p < 0.10) with child’s sex, season mester exposures than for the whole pregnancy < 2 hr/day in nonresidential outdoor environ- of conception, parity, tobacco smoke, passive period. According to these estimates, 14% of ments (n = 259), BTEX exposure both during smoking, maternal ethnicity, gestational age, the women had an average NO2 exposure > 40 the whole pregnancy period and the second µg/m3 for the entire pregnancy period, which is trimester showed a statistically significant Table 1. Characteristics of the study population the European Union limit value to come into negative effect on birth weight. Estimated (n = 570). force in 2010 (European Commission 1999). reductions in birth weight for an IQR increase Correlation coefficients among the three tri- of BTEX exposure were 76.6 g and 101.9 g Birth weight mesters ranged from 0.45 to 0.50 for NO2 and during pregnancy and the second trimester, p-Valuea Variable No. (%) (g) from 0.72 to 0.74 for BTEX, reflecting small respectively. The negative effect of NO2 expo- seasonal variation in exposure. sure variables in this subset of women was less Categorized variable Child’s sex < 0.001 Table 4 shows time–activity patterns clear but showed some stronger effects during Male 288 (50.5) 3,316 reported in the 32nd-week interview and the second trimester of pregnancy (p = 0.09). Female 282 (49.5) 3,177 referring to the entire pregnancy. Differences Because the three trimester exposures of Season of conception 0.04 between weekdays and weekends were both pollutants (particularly BTEX) were Spring 158 (27.7) 3,217 Summer 167 (29.3) 3,248 Table 2. Distribution of 9-month and trimester exposures to NO2 and BTEX (µg/m3). Fall 132 (23.2) 3,332 Winter 113 (19.8) 3,188 Pollutant (period) Mean ± SD Minimum 25th Percentile Median 75th Percentile Maximum Tobacco smoking during pregnancy < 0.001 NO2 0 467 (83.7) 3,277 9 months 32.17 ± 8.89 17.37 26.40 30.77 35.91 68.45 1–5 cigarettes/day 61 (10.9) 3,200 First trimester 32.66 ± 10.56 9.59 25.83 31.81 38.10 74.30 > 5 cigarettes/day 30 (5.4) 3,023 Second trimester 31.86 ± 10.57 10.33 24.98 30.97 36.98 77.47 Passive smoking during pregnancy 0.03 Third trimester 32.67 ± 10.60 10.18 25.19 31.81 37.66 74.37 Yes 241 (43.2) 3,207 No 317 (56.8) 3,285 BTEX 9 months 14.65 ± 5.52 3.95 10.25 14.65 18.67 27.63 Maternal parity 0.09 First trimester 14.91 ± 6.21 2.44 9.78 14.68 19.57 29.51 0 323 (56.9) 3,221 Second trimester 14.49 ± 6.05 2.69 9.42 13.82 19.46 31.30 ≥ 1 245 (43.1) 3,283 Third trimester 14.88 ± 6.24 2.62 9.86 14.03 19.58 31.69 Maternal education 0.11 Primary education 166 (29.3) 3,197 Secondary education 237 (41.8) 3,258 Table 3. Spearman correlation coefficients between estimated air pollutant’s concentrations by 9-month University degree 164 (28.9) 3,274 and trimester exposures. Maternal race/ethnicity 0.01 White/Caucasian 551 (96.8) 3,238 NO2 BTEX Latin American 14 (2.5) 3,595 9 First Second Third 9 First Second Third Black 4 (0.7) 3,136 Exposure Months trimester trimester trimester Months trimester trimester trimester Continuous variables Median IQR p-Valueb NO2 Maternal age (years) 31.1 5.7 0.43 9 months 1 Gestational age 39.9 1.9 < 0.001 First trimester 0.79 1 (weeks) Second trimester 0.79 0.50 1 Maternal height (cm) 162 8.3 0.01 Third trimester 0.80 0.45 0.46 1 Maternal prepregnancy 60 14 < 0.001 BTEX weight (kg) 9 months 0.77 0.62 0.60 0.63 1 Paternal height (cm) 175 8 0.02 First trimester 0.69 0.80 0.45 0.43 0.90 1 Paternal weight (kg) 79 15 0.01 Second trimester 0.71 0.48 0.80 0.44 0.90 0.74 1 ap-Values for comparing means by t-test or analysis of Third trimester 0.72 0.46 0.43 0.81 0.91 0.74 0.72 1 variance. bp-Values of Pearson correlation coefficients between each continuous variable and birth weight. All correlation coefficients are significantly different from 0 (p < 0.01). 1324 117 | number 8 | August 2009 • Environmental Health Perspectives ovlume