Perinatal & Pediatric
Exploring Maternal Thyroid Hormones as Mediators in the Association Between Prenatal Exposure to Endocrine Disrupting Chemicals and Child Cognition in the SELMA study Marlene Stratmann* Marlene Stratmann Chris Gennings Carl-Gustaf Bornehag
Background: Endocrine disrupting chemicals (EDCs) are associated with both thyroid hormones and neurodevelopment, yet, no previous studies have looked at the potential mediating effect of thyroid hormones on the association between EDC exposure and neurodevelopment.
Aims: To explore if the association between prenatal exposure to EDCs and child neurodevelopment is mediated by thyroid hormones, stratified by child sex and gestational age at the time of sample collection.
Methods: For 572 mother-child pairs from the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study, a mixture of 26 EDCs (phenols, phthalates,per- and polyfluoroalkyl substances and persistent chlorinated compounds) and thyroid hormones, as measured by a ratio between thyroxine (T4) and triiodothyronine (T3), were measured in maternal serum and urine. Neurodevelopment of the child was assessed with the Wechsler Intelligence Scale for Children. We used a weighted quantile sum regression index to divide the mixture into deciles and create one exposure variable. Linear regression analyses were adjusted for relevant confounders and stratified by sex, as well as early or late gestational age at time of sampling (<10 or ≥ 10 weeks gestation). Mediation was measured using the causal framework and the product method. Chemicals of concerns were identified in those that show a potential mediating effect by thyroid hormones.
Results: For boys (≥ 10 weeks gestation) the average causal mediation effect of the T4/T3 ratio was -0.32 (95% CI -0.82, 0.02), corresponding to a non-significant mediated proportion of 20%. For boys (<10 weeks gestation) and girls (<10 and ≥ 10 weeks of gestation), no mediation could be detected. Chemicals of concern for boys (≥ 10 weeks gestation) are PBA, BPF, TCP, MCiNP, MEP and MBzP.
Conclusion: These results point towards a potentially important mediating effect by TT4/TT3 ratio in the mother and a lower IQ in boys (≥ 10 weeks gestation).