The NorthMom study: population-based follow-up of women in a birth cohort to assess pregnancy exposures and effects on breast cancer risk factors.

BACKGROUND: The NorthMom Study (NorthMom) is an observational, population-based cohort designed to determine how the environment during pregnancy affects later health risks among women. The specific focus of NorthMom is breast cancer risk, evaluated through intermediate markers such as breast density, and additional outcomes may be studied in the future. METHODS: NorthMom is nested in the larger NorthPop Birth Cohort Study (NorthPop), which was initiated in Västerbotten County, Sweden in 2016 and closed recruitment in 2025. All women previously enrolled in NorthPop are invited to join NorthMom after turning 40 years of age. Women who have moved from the county, have withdrawn or declined follow-up from NorthPop, or are pregnant at the time of invitation are considered ineligible. Those who agree to participate visit the Clinical Research Center at the University Hospital of Umeå in Västerbotten, Sweden. A study nurse collects a blood sample and additional health data, including body composition by Dual-Energy X-ray absorptiometry (DXA). To assess breast density, mammographic images from the Swedish national breast cancer screening program are acquired and evaluated both manually (by a consultant radiologist) and automatically using the Laboratory for Individualized Breast Radiodensity Assessment (LIBRA) software. Measures include classification according to BI-RADS 4 (1-4) and BI-RADS 5 (A-D), as well as continuous densities (%) and dense area (cm2). Health-related and environmental exposure data are collected by NorthPop during pregnancy and requested for secondary use in NorthMom. Available exposures include geo-spatial data on ambient air pollution, traffic noise, and green environments. For subsets of women, analyses of chemicals in plasma samples collected during pregnancy are available. Additional chemical exposomics analyses and blood biomarker analyses, including proteomics and metabolomics, may be relevant in the future. DISCUSSION: Analysis of data collected as part of NorthMom and NorthPop will be used to assess relationships between environmental exposures during pregnancy and women's later health, with a focus on breast cancer risk factors such as breast density after age 40. TRIAL REGISTRATION: Registered in Researchweb, 19 August 2026 (project number 287619).