Phthalate exposure during second and third trimester of pregnancy may impact fetal growth and development: Study

Phthalate esters, or PAEs, are endocrine disruptors. Several epidemiological studies have suggested that phthalates might affect maternal thyroid hormones in utero, but results have been inconsistent. The aim of the study was to determine more clearly the relationship between phthalate exposure and thyroid hormone levels over the course of pregnancy.

In this study, 672 pregnant women were enrolled, with two urine and one blood sample collected from each participant in the course of three trimesters. Urine samples from 663, 335, and 294 women in the first, second, and third trimesters, respectively, were analyzed for seven phthalate metabolites. Blood samples from 596, 627, and 576 women in the first trimester; 292, 293, and 282 in the second trimester; and 250, 250, and 248 in the third trimester were examined for free thyroxine (FT4), thyroid-stimulating hormone (TSH), and total triiodothyronine (TT3).

The key findings of the study were:

• Other than monobenzyl phthalate (MBzP), detected in 25%-33% of samples, other metabolites were found in over 86% of urine samples, indicating widespread exposure to DEP, DBP, and DEHP.

• The phthalate exposure levels in this cohort were significantly higher than those reported in other countries.

• The levels of phthalate metabolites changed across trimesters, suggesting changing exposures and metabolic changes during pregnancy.

• There were significant linear trends for FT4, TSH, and to some degree TT3, across quartiles of specific phthalate metabolites. In the highest quartiles:

• A 2%-3.7% increase in FT4 levels associated with MEP, MECPP, MEHHP, and a number of sums of metabolites.

• Significantly, it contributes to a rise in TSH levels for all phthalate metabolites with the exception of MEHHP.

• This corresponds to an increase of 2.2% for TT3 with MEP, and a decrease of 2.7% with ΣDBP.

• Higher TSH/FT4 ratios were found with higher quartiles of the following specific phthalate metabolites: MEP, MiBP, MnBP, ∑7PAE, ∑DBP, and ∑LMW.

On the basis of these findings, inference can be made that the exposure to phthalate in utero is associated with changes in maternal thyroid hormone concentrations. This research underlines that during pregnancy, phthalate exposure should be monitored because of its possible disturbances in thyroid hormone levels, very critical for fetal development. The result reiterates the need for further confirmation of the present findings and exploring mechanisms through which phthalates may influence the action of thyroid.

Reference:

Al-Saleh, I., Elkhatib, R., Alghamdi, R., Alrushud, N., Alnuwaysir, H., Alnemer, M., Aldhalaan, H., & Shoukri, M. (2024). Phthalate exposure during pregnancy and its association with thyroid hormones: A prospective cohort study. International Journal of Hygiene and Environmental Health, 261(114421), 114421. https://doi.org/10.1016/j.ijheh.2024.114421