Heavy metals and diminished ovarian reserve: single-exposure and mixture analyses amongst women consulting in French fertility centres.

RESEARCH QUESTION: Do heavy metals affect the risk of diminished ovarian reserve (DOR) in women of reproductive age? DESIGN: A total of 139 cases and 153 controls were included between 2016 and 2020. The participants were aged between 18 and 40 years and attended consultations for couple infertility in one of four fertility centres in western France. Cases of DOR were defined as women with an antral follicle count less than 7, anti-Müllerian hormone levels 1.1 ng/ml or less, or both. Controls were frequency matched on age groups and centres, and were women with normal ovarian reserve evaluations, no malformations and menstrual cycles between 26 and 35 days. Heavy metals (lead, mercury, cadmium and chromium) were measured in whole blood at inclusion. Single-exposure associations were examined with multivariable logistic regressions adjusted on potential confounders. Mixture effects were investigated with quantile g-computation and Bayesian kernel machine regression (BKMR). RESULTS: Chromium as a continuous exposure was significantly associated with DOR in unadjusted models (OR 2.07, 95% CI 1.04 to 4.13) but the association was no longer significant when confounders were controlled for (adjusted OR 2.75, 95% CI 0.88 to 8.60). Similarly, a statistically significant association was observed for the unadjusted second tercile of cadmium exposure (OR 1.87, 95% CI 1.06 to 3.30); however, this association was no longer statistically significant after adjustment. None of the other associations tested were statistically significant. Quantile g-computation and BKMR both yielded no significant change of risk of DOR for the mixture of metals, with no evidence of interaction. CONCLUSIONS: Weak signals that some heavy metals could be associated with DOR were detected. These findings should be replicated in other studies.