A new study published online on January 17, 2015 in the peer-reviewed journal Reproductive Biology and Endocrinology investigates the relationship between urinary phthalate metabolites and maternal hormone levels at multiple time points during pregnancy. The Puerto Rico Testsite for Exploring Contamination Threats (PROTECT) project is designed to examine the relationship between various environmental contaminants and adverse pregnancy outcomes. The current study includes 106 pregnant women (aged 18-40 years) from the PROTECT cohort. Their urine and blood were collected at three separate visits. Samples collected at a gestational age of 18 ±2 and 26 ±2 weeks were analyzed for eleven phthalate metabolites (urine) and thyroid and sex hormone levels (serum). In longitudinal analyses, the authors observed inverse associations between free triiodothyronine (FT3) and mono-3-carboxypropyl phthalate (MCPP), a metabolite of several high molecular weight phthalates, and between progesterone and mono-ethyl phthalate, a metabolite of diethyl phthalate. Cross-sectional analyses by pregnancy week revealed inverse associations at the later pregnancy stage between FT3 and both MCPP and mono-carboxyisooctyl phthalate, and further between free thyroxine and metabolites of di(2-ethylhexyl) phthalate (DEHP, CAS 117-81-7).  In the EU, DEHP is authorized for use in plastic food contact and in the U.S. it is approved as an indirect food additive. The results of this study thus provide suggestive evidence that phthalate exposure in pregnancy may alter maternal thyroid and sex hormone levels. Further research is needed to elucidate the pathways through which phthalates may alter these levels, the authors stress.

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Johns, L.E. et al. (2015). “Urinary phthalate metabolites in relation to maternal serum thyroid and sex hormone levels during pregnancy: a longitudinal analysis.Reproductive Biology and Endocrinology 13:4 (open access).

PROTECT project website