Gestational Exposures to Phthalates and Folic Acid, and Autistic Traits in Canadian Children

Background: The etiology of autism spectrum disorder is poorly understood. Few studies have investigated the link between endocrine-disrupting chemicals and autistic traits. We examined the relationship between gestational phthalates and autistic traits in 3- to 4-y-old Canadian children. We also investigated potential effect modification by sex and folic acid supplementation. Methods: We enrolled 2,001 women>18  years of age during the first trimester of pregnancy between 2008 and 2011 from 10 cities in Canada. At 3–4 years of age, 610 children underwent neuropsychological assessments including the Social Responsiveness Scale–II (SRS-2) as a measure of autistic traits and social impairment. We measured 11 phthalate metabolites in maternal first trimester urine samples and assessed folic acid supplementation from reported intakes. We estimated covariate-adjusted differences in SRS-2 T-scores with a doubling in phthalate concentrations in 510 children with complete data. Results: Mean total SRS T-score was 45.3 (SD=6.1). Children with higher gestational exposure to mono-n-butyl (MBP) and mono-3-carboxypropyl (MCPP) concentrations exhibited significantly higher total SRS T-scores, indicating greater overall social impairment, as well as higher scores on subdomains, indicating deficits in social cognition, social communication, social motivation, and restricted interests/repetitive behaviors. A doubling in MBP or MCPP concentrations was associated with 0.6 (95% CI: 0.1, 1.0) and 0.5 (95% CI: 0.1, 0.8) higher total SRS T-scores. Associations were consistently and significantly stronger in boys (βMBP=1.0; 95% CI: 0.4, 1.6; n=252) compared with girls (βMBP=0.1; 95% CI: −0.6, 0.7; n=258) and among children who had lower prenatal folic acid supplementation (<400μg/d) (βMBP=1.3; 95% CI: 0.4, 2.3; n=59) compared with those who had adequate folic acid supplementation (≥400μg/d) (βMBP=0.4; 95% CI: −0.1, 0.8; n=451). Conclusions: Higher gestational concentrations of some phthalate metabolites were associated with higher scores of autistic traits as measured by the SRS-2 in boys, but not girls; these small size effects were mitigated by first trimester-of-pregnancy folic acid supplementation. https://doi.org/10.1289/EHP5621

. Sociodemographic and perinatal factors among MIREC participants who completed the SRS (n=601) compared to those who enrolled at the beginning of study in the same 7 study sites (n=1590). Table S2. Distribution of maternal SG-standardized urinary phthalates metabolites (in µg/L). Table S3. Associations between maternal SG-standardized urinary phthalate concentrations (for a two-fold increase) and children's SRS-2 T-scores at 3-4 years, stratified by folic acid (FA) supplementation during pregnancy. Table S4. Associations between maternal SG-standardized urinary phthalate concentrations and children's SRS-2 T-scores at 3-4 years, with adjustment for additional predictors of SRS scores. β represents the change in point score for a two-fold increase in urinary phthalate concentration. Table S5. Sex-stratified associations between maternal SG-standardized urinary phthalate concentrations and children's SRS-2 T-scores at 3-4 years. β represents the change in point score for a two-fold increase in urinary phthalate concentration. Table S6. Associations between maternal urinary phthalate concentrations and children's SRS-2 T-scores at 3-4 years, with adjustment for specific gravity as an independent predictor in the models. β represents the change in point score for a two-fold increase in urinary phthalate concentration. Figure S1. Flow chart of the study participants. Figure S2. Directed acyclic graph representing the associations between phthalates, autistic traits, and potential confounders. Figure S3. Minimum set of covariates sufficient to identify the potential effect of phthalates on autistic traits. Red squares indicate the variables to adjust for. Figure S4. Exposure-response relationship and 95% confidence intervals for the associations between maternal SG-standardized urinary MCPP concentrations and child SRS T-scores at 3-4 years. DF: degrees of freedom for the smooth term; p-values for significance (p) were derived with Wald tests using the Bayesian covariance matrix for the coefficients and departure from linearity (p-departure) were derived by comparing the models with urinary phthalate concentrations introduced as a spline function and as a linear term. Figure S5. Exposure-response relationship between maternal SG-standardized urinary phthalates concentrations and child total SRS T-scores at 3-4 years, by child sex. Figure S6. Difference (95% CI) for a two-fold increase in maternal SG-standardized urinary phthalate concentrations in relation to children's SRS-2 T-scores at 3-4 years, using Inverse probability censoring weights to adjust for potential selection bias. β represents the change in point score for a two-fold increase in urinary phthalate concentration. Significant effectmodification by sex at p<0.1 is indicated by red asterisks. Figure S7. Difference (95% CI) for a two-fold increase in maternal SG-standardized urinary phthalate concentrations in relation to children's SRS-2 T-scores at 3-4 years, stratified by folic acid supplementation during pregnancy categorized into three categories (<400 µg/day; 400-999 µg/day; ≥1000 µg/day).   Table S3: Associations between maternal SG-standardized urinary phthalate concentrations (for a twofold increase) and children's SRS-2 T-scores at 3-4 years, stratified by folic acid (FA) supplementation during pregnancy.

SRS subscale Phthalate
Inadequate folate status (<400µg/day) Social Communication  All models were adjusted for study city, child sex, household income, maternal education, maternal age, parity, marital status, race/ethnicity, and year of enrollment. Corresponding estimates and 95% CI are provided in Figure 3. p-phthalate X FA: p-value for the interaction between phthalates concentrations and FA supplementation (<400µg/day / ≥400µg/day). Table S4: Associations between maternal SG-standardized urinary phthalate concentrations and children's SRS-2 T-scores at 3-4 years, with adjustment for additional predictors of SRS scores. β represents the change in point score for a two-fold increase in urinary phthalate concentration.

SRS subscale Phthalate
All All models were adjusted for study city, child sex, household income, maternal education, maternal age, parity, marital status, race/ethnicity, folic acid supplementation, year of enrollment, smoking during pregnancy, alcohol during pregnancy, 1 st trimester blood lead concentrations, admission at a neonatal intensive care unit, Home Observation and Measurement of the Environment (HOME) scores, and exclusive breastfeeding duration. p-phthalate X Sex: p-value for the interaction term between phthalates concentrations and Sex in the models.  All models were adjusted for study city, household income, maternal education, maternal age, parity, marital status, race/ethnicity, folic acid supplementation, and year of enrollment. p-difference corresponds to the comparison of d/SE d to the standard normal distribution, where d is the difference between the two estimates, and is the standard error of the difference. Table S6: Associations between maternal urinary phthalate concentrations and children's SRS-2 T-scores at 3-4 years, with adjustment for specific gravity as an independent predictor in the models. β represents the change in point score for a two-fold increase in urinary phthalate concentration

SRS subscale Phthalate
All Boys Girls pphthalate X Sex β (95% CI) p-value β (95% CI) β (95% CI) Total SRS Score All models were adjusted for study city, household income, maternal education, maternal age, parity, marital status, race/ethnicity, folic acid supplementation, specific gravity, and year of enrollment. pphthalate X Sex: p-value for the interaction term between phthalates concentrations and Sex in the models. Figure S1: Flow chart of the study participants. Figure S2. Directed acyclic graph representing the associations between phthalates, autistic traits, and potential confounders Figure S3. Minimum set of covariates sufficient to identify the potential effect of phthalates on autistic traits. Red squares indicate the variables to adjust for. Figure S4: Exposure-response relationship and 95% confidence intervals for the associations between between maternal SG-standardized urinary MCPP concentrations and child SRS T-scores at 3-4 years.
DF: degrees of freedom for the smooth term; p-values for significance (p) were derived with Wald tests using the Bayesian covariance matrix for the coefficients and departure from linearity (p-departure) were derived by comparing the models with urinary phthalate concentrations introduced as a spline function and as a linear term. Figure S5: Exposure-response relationship between maternal SG-standardized urinary phthalates concentrations and child total SRS T-scores at 3-4 years, by child sex Figure S6: Difference (95% CI) for a two-fold increase in maternal SG-standardized urinary phthalate concentrations in relation to children's SRS-2 T-scores at 3-4 years, using Inverse probability censoring weights to adjust for potential selection bias. β represents the change in point score for a two-fold increase in urinary phthalate concentration. Significant effect-modification by sex at p<0.1 is indicated by red asterisks. Figure S7: Difference (95% CI) for a two-fold increase in maternal SG-standardized urinary phthalate concentrations in relation to children's SRS-2 T-scores at 3-4 years, stratified by folic acid supplementation during pregnancy categorized into three categories (<400 µg/day; 400-999 µg/day; ≥1000 µg/day).