Size- and hydrophobicity-dependent accumulation of microplastics in follicular fluid is linked to impaired ovarian reserve in women undergoing medically assisted reproduction

<title>Abstract</title> Microplastics (MPs) are emerging contaminants with potential impacts on human fertility. We quantified MP concentrations in follicular fluid and matched blood samples from women undergoing medically assisted reproduction, and evaluated their association with reproductive outcomes. MPs were detected in the follicular fluid of nearly all women. Higher concentrations were significantly associated with reduced oocyte yield and an estimated odds of becoming pregnant reduced by a factor of 0.99 for every additional particle per mL. While MP profiles overlapped between blood and follicular fluid, several hydrophobic polymers and bigger MPs were significantly reduced in follicular fluid, suggesting selective translocation. Notably, the correlation between follicular fluid and blood MP levels suggests that blood-based monitoring could offer a non-invasive proxy for ovarian exposure and associated fertility risk. These findings provide clinical evidence that MPs selectively accumulate in the ovary and are linked to impaired ovarian reserve.