Individual and joint effects of phthalates exposure on the risk of early miscarriage

The exposure levels of phthalates in humans have dropped dramatically. Little is known about the individual and joint effects of phthalates exposure at low levels on the risk of early miscarriage.

To examine the association between exposure to phthalates individually or as a mixture and early miscarriage.

A case-control study was conducted in Shanghai, China during 2019-2020. A total of 291 women seeking medical services due to miscarriage (cases) and 308 women planning to terminate an unintended pregnancy (controls) within 12 gestational weeks were recruited. Urinary concentrations of eight phthalate metabolites were determined by ultra-performance liquid chromatography. We included 534 women in the main analysis who had available data on both phthalates exposure and complete information on potential confounders. We used logistic regression and Bayesian kernel machine regression (BKMR) to examine the associations of concentrations of phthalates with miscarriage.

Among the phthalate metabolites, mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) had the highest concentration (8.10 ng/mL), followed by mono(2-ethyl-5-oxohexyl) phthalate (MEOHP, 2.68 ng/mL) and monobutyl phthalate (MBP, 2.24 ng/mL). Higher concentrations of MBP, mono(2-ethylhexyl) phthalate (MEHP), MEHHP, MEOHP and the molar sum of di(2-ethylhexyl) phthalate (DEHP) metabolites (∑DEHPm) were associated with an increased risk of miscarriage exhibiting a dose-response relationship. The most evident association of miscarriage was found with ∑DEHPm, with adjusted odds ratio (95% confidence interval) of 1.94 (1.14, 3.31) for the second quartile, 2.83 (1.67, 4.79) for the third quartile and 4.28 (2.49, 7.37) for the fourth quartile compared to the first quartile. Consistently, the phthalate mixture was positively associated with the risk of miscarriage and DEHP was the predominant contributor to the joint effect in BKMR model.

Phthalates are a family of synthetic chemicals mainly used as plasticizers, solvents and additives in a large variety of industrial and consumer products, including food packing materials, toys, gloves, medical devices and personal care products. Although exposure levels of phthalates of pregnant women have declined sharply over the past few decades, phthalates exposure was still associated with an increased risk of early miscarriage. Our findings suggest that future researchers and policy makers might need to take low-dose effects of phthalates into account regarding the reproductive toxicity of phthalates exposure in humans.

Our findings contribute to the awareness of the reproductive toxic potential of phthalates at low levels in humans and support the ongoing efforts to further reduce exposure to phthalates.