Effects of organophosphate esters on thyroid function during pregnancy: Risk of endocrine disruptors during early- and mid-pregnancy.

Organophosphate esters (OPEs) can disrupt thyroid function, but the association between OPEs and thyroid function is limited. In this study, the association between OPEs and thyroid hormones (THs) was studied. The study population was comprised of two groups: early-pregnancy and mid-pregnancy. The results showed that in all-pregnancies group, tri-n-butyl-phosphate (TNBP) and tris(2-chloroisopropyl) phosphate (TCIPP) were positively correlated with thyroid-stimulating hormone (TSH) levels, whereas tris(2-chloroethyl) phosphate (TCEP) was positively correlated with the free thyroxine (FT4)/free triiodothyronine (FT3) ratio. In early-pregnancy group, 2-ethylhexyl diphenyl phosphate (EHDPP) and tris(2-ethylhexyl) phosphate (TEHP) were correlated with FT3 and FT4 levels, respectively. TNBP was positively correlated with TSH levels, and TEHP was negatively correlated with FT4/FT3 ratio. In the mid-pregnancy group, no significant association was observed between OPEs and THs. Restricted cubic spline analysis revealed that, in all-pregnancies group, TNBP, tris (methylphenyl) phosphate (TMPP), and TCIPP were correlated with TSH/FT4 ratios, reflecting homeostasis of the hypothalamic-pituitary-thyroid (HPT) axis. In early-pregnancy group, TNBP was correlated with TSH/FT4 ratios and TCIPP was correlated with TSH levels. These associations exhibited L-shaped relationship. However, the overall effect of total OPEs on THs levels was not significant. In addition, TPOAb statue could alter the association between OPEs and THs. These findings indicated that OPEs could disrupt maternal THs homeostasis and interfere with the HPT axis, requiring additional human-supported experiments to explore OPE-induced thyroid disruption mechanisms.