Lessons learned from longitudinal biomonitoring and birth cohort studies: informing the future of reproductive health research in Canada

Longitudinal biomonitoring studies during preconception, pregnancy and early childhood are highly valuable tools for assessing environmental chemical exposures during sensitive windows and their effects on health and development. For the past 15 years, the Maternal-Infant Research on Environmental Chemicals (MIREC) Research Platform has been Canada's flagship study of the long-term effects of early life exposure to environmental chemicals. In light of the evolving scientific and legislative landscapes and need to address emerging research questions, MIREC Platform researchers at Health Canada consulted with scientific investigators of other cohort studies to inform the development of a future preconception or pregnancy longitudinal biomonitoring study. This effort included 1) hybrid consultation meetings on Dec 6, 2024 (Toronto, ON) and Jan 21, 2025 (Ottawa, ON) and 2) a virtual seminar series from October 2024 to June 2025 hosted by the Health Canada MIREC team. Our objective here is to share lessons learned from this consultation. We report on key lessons learned related to the themes of: 1) participant engagement, recruitment and retention, 2) validity and causal inference, and 3) study longevity. While the ultimate goal of this consultation was to inform future longitudinal biomonitoring studies in Canada, the content is largely generalizable and relevant to others planning, modifying, or evaluating observational research in reproductive and environmental epidemiology.