Older Maternal Age, Chlorinated Solvent Emissions, and Selected Birth Defects in Offspring

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Older maternal age has been observed to modify associations between maternal residential proximity to industrial air emissions of solvents and birth defects in offspring. However, the number of older women in these studies has been insufficient to examine such associations with specific solvents. Using data from the Texas Birth Defects Registry for births occurring in 1996-2008, we examined the relation between residential proximity to industrial releases of chlorinated solvents and birth defects (neural tube, oral cleft, and heart defects) in offspring of 60,613 case-mothers and 244,927 control-mothers. Exposures were estimated with metrics that took into account residential distances to industrial sources and annual amounts of chemicals released. Relative to exposure indices of 0, we observed the following significant additive and multiplicative interactions (p < 0.05) by maternal age (< 35 years, 35+ years, respectively): oral cleft defects with carbon tetrachloride (odds ratios [ORs] 1.02 vs.1.66) and methylene chloride (ORs 1.02 vs.1.38); cleft palate with 1,2-dichloroethylene (ORs 0.75 vs. 2.54); and cleft lip with methylene chloride (ORs 1.02 vs.1.53), tetrachloroethane (ORs 0.79 vs.1.57), trichloroethylene (ORs 1.02 vs.1.39), and any chlorinated solvent (ORs 0.97 vs. 1.37). The 95% confidence intervals for the ORs associated with older mothers excluded 1.00. Furthermore, significant additive interactions by maternal age were observed for oral clefts with 1,2-dichloroethane, ethyl chloride, and 1,2,3-trichloropropane. Older maternal age also modified some associations between chlorinated solvents and neural tube and heart defects, most notably between carbon tetrachloride and neural tube defects combined (ORs 1.31 vs. 2.46) and between trichloroethylene and obstructive heart defects (ORs 0.97 vs. 1.43). In conclusion, older maternal age may strengthen associations between chlorinated solvent emissions and selected birth defects in offspring.