Cumulative risk factor burden and stillbirth: insights from real-world data

To develop a stillbirth risk index based on cumulative burden of pre-pregnancy and early-pregnancy risk factors, to assist clinicians in planning antenatal care. This population-based cohort study used data from the Medical Birth Registry of Norway and Statistics Norway from 1999 to 2022. All individuals with singleton pregnancies in Norway who gave birth from gestational age ≥ 22 weeks were included, resulting in a study population of 1 350 936 births. Fifteen pre-pregnancy and early-pregnancy characteristics associated with ≥ 25% higher stillbirth rate compared to the total study population and with odds ratios ≥ 1.5 were included in the risk index. These were: Maternal age ≥35 years, maternal country of birth in South Asia, Sub-Saharan Africa or unknown, education (none or compulsory or unknown), not being married/cohabitating, chronic hypertension, type 1 or 2 diabetes, parity ≥4, previous stillbirth, previous second trimester loss, daily smoking in first trimester, and lack of folic acid use during pregnancy. There were 4941 (0.37%) stillbirths registered. Stillbirth rates increased with cumulative risk factor burden from 2.08 per 1000 births in individuals with none of the chosen risk factors to 13.61 in individuals with risk score ≥ 5. Odds ratios increased parallel from 1.58 (95% confidence interval 1.46–1.71) in individuals with risk score 1 to 6.62 (95% CI 5.62–7.78) in individuals with risk score ≥ 5. These patterns were consistent across two subperiods (1999–2010 and 2011–2022). Cumulative burden of pre-pregnancy and early‑pregnancy risk factors can stratify individuals into meaningful risk groups, supporting tailored antenatal care.