Maternal Exposure to Metals and Time-to-Pregnancy: Results From the Maternal-Infant Research on Environmental Chemicals (MIREC) Pregnancy Cohort

Introduction: Environmental exposure to metals is a public health concern given their ubiquitous nature in the environment. Many of these metals are suggested to be endocrine-disrupting chemicals and have demonstrated adverse effects on women’s reproductive health, including irregular menstrual cycles, endometriosis, and infertility. However, there is weak evidence exploring the relationship between metals and fecundity, as measured by time-to-pregnancy (TTP), with previous studies showing inconsistent results. This thesis evaluates the association between metals (arsenic, cadmium, lead, manganese and mercury), TTP, and infertility in female participants from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. Methods: Chemical concentrations were measured in maternal blood during the first trimester of pregnancy. TTP in months was ascertained retrospectively, via self-report. Cox proportional hazards models modified for discrete-time data were used to calculate fecundability odds ratios (FORs) and 95% confidence intervals (CI) for the association between metal concentrations and TTP. Logistic regression generated odds ratios (ORs) for the association between metals and infertility. Models were adjusted for maternal age, pre-pregnancy BMI, education, income, recruitment site, and plasma lipids. Results: Exposure to arsenic, cadmium, manganese, or mercury was not associated with TTP or infertility. Increments of one standard deviation of lead concentrations resulted in a shorter TTP (adjusted FOR 1.08, 95% CI 1.01 – 1.16); however, the association was not linear when exposure was modeled in tertiles. For manganese, relative to the first tertile, the third tertile was associated with a decreased odds of infertility (adjusted OR 0.65; 95% CI 0.43 – 0.97); however this association was not observed for TTP. Conclusion: Results support that at current environmental levels of exposure, metals are not associated with decreased fecundability or infertility. This research adds to the limited body of ...