Maternal Occupational Exposure to PAHs
Maternal Occupational Exposure to PAHs
Participation in the NBDPS was 71% among gastroschisis case mothers and 68% among control mothers. Of the 418 case mothers and 4,116 control mothers (n = 4,534) included in the NBDPS for the period 1997–2002, 73% were employed for at least 1 month during the critical window of exposure (the remaining 37% reported no job during the critical window), leaving 299 gastroschisis case infants and 2,993 control infants (n = 3,292) eligible for this analysis. Selected maternal characteristics are summarized by case–control status, along with the crude OR and 95% CI for each factor and gastroschisis, in Table 1. Compared with control mothers, mothers of cases were less likely to be ≥ 20 years of age, to be obese versus having normal BMI, or to have one or more previous births, an education level beyond high school, or gestational diabetes; and they were more likely to be light, moderate, or heavy smokers, to be exposed to secondhand smoke at home or work, and to have three or more jobs in the month before conception through the third month of pregnancy. There were no significant differences in the mean time to interview between case and control mothers (11.3 vs. 10.3 months, p = 0.32) or between PAH-exposed and unexposed mothers (11.3 vs. 11.4 months, p = 0.67).
The exposure assessment yielded few discordant ratings between industrial hygienists in exposure assignment. Specifically, 250 mother jobs were discordant for the estimated PAH exposure rating among 12,492 (2%) included in the entire NBDPS (i.e., all cases and controls included in the NBDPS occupational PAH exposure assessment) (Rocheleau et al. 2011).
Table 2 displays the distributions of jobs within the 23 SOC major job groups held by mothers of cases and controls stratified by exposure status. Jobs in the sales and related occupations SOC job group were the most frequent held jobs among exposed case mothers (13 of 28 individual jobs held by exposed case mothers during the critical window), including 12 jobs as cashiers in fast food restaurants. The second largest SOC job group with PAH exposure among exposed case mothers was food preparation and serving related occupations (n = 11). The most common jobs among exposed control mothers were in food preparation and serving related occupations (52 of 109 individual jobs), followed by sales and related occupations (n = 32).
Overall, the prevalence of estimated occupational PAH exposure was 9% in case mothers (27 of 299) and 4% in control mothers (107 of 2,993), and there was a significant (p < 0.001) crude association between estimated maternal occupational exposure to PAHs and gastroschisis in offspring (OR = 2.68; 95% CI: 1.72, 4.16) (Table 3). When we restricted our analysis to those mothers who had jobs rated with high confidence (n = 282 case mothers; n = 2,937 control mothers), the crude association was similar to that obtained in the full group (OR = 2.63; 95% CI: 1.68, 4.11). Additionally, there was a significant association (p = 0.03) between estimated maternal occupational exposure to PAHs and gastroschisis in offspring after adjusting for maternal age, BMI, education, gestational diabetes, maternal smoking, and study center (OR = 1.75; 95% CI: 1.05, 2.92).
Although the association between maternal occupational exposure to PAHs and gastroschisis in offspring among mothers who were < 20 years of age was not significant (adjusted OR = 1.14; 95% CI: 0.55, 2.33), there was a significant association among mothers ≥ 20 years of age (OR = 2.53; 95% CI: 1.27, 5.04) after adjusting for maternal BMI, education, gestational diabetes, maternal smoking, and study center (variables associated with gastroschisis and maternal occupational exposure) (Table 3). The association among mothers who were ≥ 20 years of age was similar when we restricted the analysis to mothers with jobs that were rated with high confidence (adjusted OR = 2.67; 95% CI: 1.34, 5.34). When results were stratified on maternal smoking, the association was stronger among nonsmoking mothers than among those who smoked at any time during the month before conception through the third month of pregnancy (Table 3). However, this difference was minimized after adjusting for maternal age, BMI, education, gestational diabetes, and study center (nonsmokers: OR = 1.82; 95% CI: 0.94, 3.51; smokers: OR= 1.16; 95% CI: 0.51, 2.66). Finally, all analyses were repeated among isolated case infants (n = 275) and control infants, and there was no difference in our results (crude OR = 2.70; 95% CI: 1.72, 4.23).
Results
Participation in the NBDPS was 71% among gastroschisis case mothers and 68% among control mothers. Of the 418 case mothers and 4,116 control mothers (n = 4,534) included in the NBDPS for the period 1997–2002, 73% were employed for at least 1 month during the critical window of exposure (the remaining 37% reported no job during the critical window), leaving 299 gastroschisis case infants and 2,993 control infants (n = 3,292) eligible for this analysis. Selected maternal characteristics are summarized by case–control status, along with the crude OR and 95% CI for each factor and gastroschisis, in Table 1. Compared with control mothers, mothers of cases were less likely to be ≥ 20 years of age, to be obese versus having normal BMI, or to have one or more previous births, an education level beyond high school, or gestational diabetes; and they were more likely to be light, moderate, or heavy smokers, to be exposed to secondhand smoke at home or work, and to have three or more jobs in the month before conception through the third month of pregnancy. There were no significant differences in the mean time to interview between case and control mothers (11.3 vs. 10.3 months, p = 0.32) or between PAH-exposed and unexposed mothers (11.3 vs. 11.4 months, p = 0.67).
The exposure assessment yielded few discordant ratings between industrial hygienists in exposure assignment. Specifically, 250 mother jobs were discordant for the estimated PAH exposure rating among 12,492 (2%) included in the entire NBDPS (i.e., all cases and controls included in the NBDPS occupational PAH exposure assessment) (Rocheleau et al. 2011).
Table 2 displays the distributions of jobs within the 23 SOC major job groups held by mothers of cases and controls stratified by exposure status. Jobs in the sales and related occupations SOC job group were the most frequent held jobs among exposed case mothers (13 of 28 individual jobs held by exposed case mothers during the critical window), including 12 jobs as cashiers in fast food restaurants. The second largest SOC job group with PAH exposure among exposed case mothers was food preparation and serving related occupations (n = 11). The most common jobs among exposed control mothers were in food preparation and serving related occupations (52 of 109 individual jobs), followed by sales and related occupations (n = 32).
Overall, the prevalence of estimated occupational PAH exposure was 9% in case mothers (27 of 299) and 4% in control mothers (107 of 2,993), and there was a significant (p < 0.001) crude association between estimated maternal occupational exposure to PAHs and gastroschisis in offspring (OR = 2.68; 95% CI: 1.72, 4.16) (Table 3). When we restricted our analysis to those mothers who had jobs rated with high confidence (n = 282 case mothers; n = 2,937 control mothers), the crude association was similar to that obtained in the full group (OR = 2.63; 95% CI: 1.68, 4.11). Additionally, there was a significant association (p = 0.03) between estimated maternal occupational exposure to PAHs and gastroschisis in offspring after adjusting for maternal age, BMI, education, gestational diabetes, maternal smoking, and study center (OR = 1.75; 95% CI: 1.05, 2.92).
Although the association between maternal occupational exposure to PAHs and gastroschisis in offspring among mothers who were < 20 years of age was not significant (adjusted OR = 1.14; 95% CI: 0.55, 2.33), there was a significant association among mothers ≥ 20 years of age (OR = 2.53; 95% CI: 1.27, 5.04) after adjusting for maternal BMI, education, gestational diabetes, maternal smoking, and study center (variables associated with gastroschisis and maternal occupational exposure) (Table 3). The association among mothers who were ≥ 20 years of age was similar when we restricted the analysis to mothers with jobs that were rated with high confidence (adjusted OR = 2.67; 95% CI: 1.34, 5.34). When results were stratified on maternal smoking, the association was stronger among nonsmoking mothers than among those who smoked at any time during the month before conception through the third month of pregnancy (Table 3). However, this difference was minimized after adjusting for maternal age, BMI, education, gestational diabetes, and study center (nonsmokers: OR = 1.82; 95% CI: 0.94, 3.51; smokers: OR= 1.16; 95% CI: 0.51, 2.66). Finally, all analyses were repeated among isolated case infants (n = 275) and control infants, and there was no difference in our results (crude OR = 2.70; 95% CI: 1.72, 4.23).
