Intrauterine Exposure to Phthalates and Child Growth in the First Year of Life: Results from the BiTwin Cohort

Phthalates are among the endocrine-disrupting compounds with higher widespread in daily life. Our objective was to assess the associations between maternal exposure to phthalates assessed by urinary phthalate metabolites and growth at birth and in the first year of life. The BiTwin cohort (479 single and 246 multiple pregnancies) was recruited as part of the HEALS project (2017-2019). Evaluations were conducted at birth, 4, 8, and 12 months after childbirth. To mitigate the dependency on twins, we randomly selected one child per family. Birth weight was abstracted from clinical files, and parameters for the first year were based on the child health book. The maternal urine was collected at birth, and phthalate metabolites were determined by liquid chromatography coupled to tandem mass spectrometry. The association between weight growth curves and phthalates was estimated by fixed regression coefficients and 95% confidence intervals calculated through linear mixed effects models. All models include a fixed effect for time and time square and a random intercept and slope by individual. For birth weight, after adjustment, overall, a negative association was found but only statistically significant for mono-n-butyl phthalate metabolite beta = - 0.195 (95% CI - 0.372; - 0.018). In general, the results are similar by sex, but for di(2ethylhexyl) phthalate and cyclohexane-1,2-dicarboxylate, we found associations in the opposite directions. Regarding growth trajectories for the first year of life, overall, no statistically significant associations were found. However, the sum of di(2ethylhexyl) phthalate metabolites presented a positive statistically significant association beta = 0.062 (95%CI 0.002; 0.121) after further adjustment for breastfeeding duration. A positive association was also found for Mono-iso-butyl phthalate in males (beta = 0.236 (95%CI 0.063; 0.409)). Higher maternal phthalate concentrations tended to be associated with lower birth weight, although they did not reach statistical significance. Regarding the first year of life, di(2ethylhexyl) phthalate presented a positive statistically significant association with growth.