Epidemiological Studies on Fetal Loss – Better Data and Research Methods are Needed

Jørn Olsen,1 Zeyan Liew2 1Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus N 8200, Denmark; 2Department of Environmental Health Sciences, Yale School of Public Health, Yale Center for Perinatal, Pediatric, and Environmental Epidemiology, Yale School of Public Health, New Haven, CT 06510, USACorrespondence: Zeyan LiewDepartment of Environmental Health Sciences, Yale School of Public Health, Yale Center for Perinatal, Pediatric, and Environmental Epidemiology, Yale School of Public Health, 60 College Street, New Haven, CT 06510, USATel +1 203-764-9727Email zeyan.liew@yale.eduAbstract: In perinatal epidemiology, fetal deaths occur over the first timeline, from conception to birth or fetal death. Majority of other epidemiological research on human diseases focus on the second timeline, from birth to death. The transition from the first to the second timeline is not a fixed duration of time and it depends on when birth occurs. We discussed the complications when switching from the first to the second timeline in epidemiological studies of early life exposures, pregnancy events, and future health outcomes. Population-based studies often lack accurate data on the date of conception for most pregnancies and the complete count of fetal death, leading to chances for selection and misclassification biases. To address these problems, better research data and methodological advancement in study designs and biases evaluations are needed.Keywords: fetal loss, miscarriage, bias, birth cohort, epidemiology