Urinary phthalate metabolites and ovarian reserve among women seeking infertility care

Are urinary phthalate metabolites associated with reduced antral follicle growth among women in an infertility setting?

Higher urinary concentrations of di(2-ethylhexyl) phthalate (DEHP) metabolites were associated with significant decreases in antral follicle count (AFC) among women seeking infertility care.

Experimental animal studies show that DEHP accelerates primordial follicle recruitment and inhibits antral follicle growth. Whether phthalates also reduce the growing antral follicle pool in humans remains unknown.

We examined the association between urinary phthalate metabolites and AFC using prospective data from 215 females recruited between 2004 and 2012 in the Environment and Reproductive Health (EARTH) study.

We quantified the urinary concentrations of 11 phthalate metabolites. We estimated the geometric mean for all urine samples provided prior to unstimulated day 3 AFC assessment for each woman. We evaluated the association of AFC with ∑DEHP (molar sum of four DEHP metabolites) and individual phthalate metabolites using Poisson regression, adjusting for age, BMI and smoking.

We observed significant decreases in mean AFC for all higher quartiles of ∑DEHP as compared with the lowest quartile. Compared with women in the first quartile of ∑DEHP, women in the second, third and fourth quartiles had a -24% (95% confidence interval (CI): -32%, -16%), -19% (95% CI: -27%, -9%), and -14% (95% CI: -23%, -5%) decrease in mean AFC. The absolute mean AFC in the first quartile was 14.2 follicles (95% CI: 13.2, 15.2) compared with 10.7 follicles (95% CI: 9.9, 11.6) in the second quartile. We observed similar trends among the four individual DEHP metabolites. There was no consistent change in AFC among the remaining phthalate metabolite concentrations evaluated.

We demonstrated a negative association between DEHP and a well-established marker of ovarian reserve among a subfertile population. However these findings may not be generalizable to women without fertility concerns, and we cannot rule out co-exposure to other chemicals.

Environmental chemicals that inhibit the size of the growing antral follicle pool can impair fertility and reduce fecundity. This study suggests evidence in need of further investigation on the impact of phthalates on the human oocyte and follicular development.

Work supported by grants ES009718, ES022955, ES000002, and T32ES007069 from the National Institute of Environmental Health Sciences (NIEHS) and grant T32 DK007703-16 from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). C.M. was supported by a post-doctoral training award from the Canadian Institutes of Health Research. There are no competing interests to declare.