A mixture analysis of urinary microplastic levels and risk of gestational diabetes

Microplastic (MP) pollution is increasingly recognised as a pressing global environmental and public health concern, with mounting evidence suggesting its potential to disrupt metabolic processes. Pregnant women represent a particularly susceptible population, as physiological changes during gestation may amplify vulnerability to environmental toxicants. Despite these concerns, no prior studies have directly examined the relationship between internal MP exposure and glucose metabolism during pregnancy. Specifically, we aimed to assess the relationship between urinary MP concentrations and key glycemic indicators in pregnant women, offering novel insights into the potential metabolic consequences of MP exposure during this sensitive period of development.

We conducted a cross-sectional study of 3775 pregnant women (24-28 weeks of gestation) between June 2022 and March 2023. Morning urine samples were collected and analysed for microplastic particles (polyamide [PA], polypropylene [PP], polyvinyl chloride [PVC], and polyethylene [PE]). Glycemic status was assessed using fasting plasma glucose (FPG), 1-hour (1 h-OGTT), and 2-hour (2 h-OGTT) post-load glucose levels. Multivariable linear regression, Bayesian Kernel Machine Regression (BKMR), g-computation (g-comp), and quantile-based weighted quantile sum (qWQS) regression were applied to evaluate associations and mixture effects, adjusting for relevant covariates.

In adjusted linear regression models, higher urinary PA and PP concentrations were significantly associated with elevated FPG and 1 h-OGTT levels (p < 0.05). G-comp estimated that a one-quartile increase in the MP mixture was associated with significant increases in all glycemic markers. qWQS regression confirmed a positive mixture effect, with PA contributing the most weight to the index. BKMR analysis supported these findings and revealed non-linear exposure-response relationships between urinary microplastic exposure and glycemic markers. Specifically, higher overall urinary MP concentrations were associated with progressively elevated FPG and 2 h-OGTT levels, with statistically significant increases observed at the upper exposure quartiles. Associations with 1 h-OGTT were less consistent, showing some increase at higher exposure levels but with wider confidence intervals. Analysis of individual microplastic polymers indicated generally modest effects, with PVC showing a potential positive association at higher concentrations, while other polymers exhibited minimal or inconsistent associations.

Our study provides novel evidence linking urinary microplastic exposure to impaired glucose regulation during pregnancy.