Associations of phthalate metabolites in urine and follicular fluid with endometrial thickness in the TREE cohort.

Endometrial thickness (EMT) is a crucial indicator of female fecundity and pregnancy success. Experimental studies have suggested that phthalates can disrupt EMT by exerting estrogenic effects or affecting the expression of related receptors, but human evidence is scarce. We aimed to explore the relationships of phthalate metabolites in paired urine and follicular fluid (FF) with EMT among 548 women undergoing assisted reproductive technology (ART). In single-pollutant analyses, all urinary di(2-ethylhexyl) phthalate (DEHP) metabolites were positively linked with follicular phase EMT (all p for trends ≤ 0.01) and higher risks of thick EMT (all p for trends ≤ 0.10). Meanwhile, mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) in FF showed similar positive associations (both p for trends ≤ 0.01). Bayesian kernel machine regression (BKMR) models revealed that phthalate mixtures in urine and FF were positively associated with follicular phase EMT or the risk of thick EMT. Our results indicated that DEHP exposure may increase EMT among women undergoing ART.