Preconception computed tomography exposure and risk of stillbirth in a nationwide population based cohort study

Fetal radiation exposure can cause pregnancy loss, malformation, growth disturbance, and mutagenic/carcinogenic effects. Insufficient guidance on radiation protection for women of childbearing age complicates risk assessment. This population-based retrospective cohort study investigated preconception CT radiation on stillbirths using Taiwan National Health Insurance Database from 1995 to 2018. A total of 1,218,744 births (live and stillbirth) of 940,280 women were eligible, including 1,179,443 live births of 913,811 women in the control group and 13,631 stillbirths(≥ 20 weeks of gestation or weight ≥ 500 g) of 13,046 women in the study group. CT exposure within 90 days, 1 year, 3 years, and 5 years before conception occurred in 0.6%, 2.5%, 6.1%, and 9.0% of stillbirth mothers, versus 0.5%, 2.1%, 5.4%, and 8.1% of controls. In adjusted analyses, CT exposure within 1 year (aOR = 1.14; 95% CI: 1.01-1.28; p = 0.0325) and 3 years (aOR = 1.08; 95% CI: 1.00-1.17; p = 0.0482) before pregnancy was modestly associated with stillbirth, while the 90-day (aOR = 1.12; 95% CI: 0.88-1.42; p = 0.355) and 5-year (aOR = 1.06; 95% CI: 0.99-1.13; p = 0.0917) windows were not significant. These small effect sizes, together with potential residual confounding and lack of consistent dose-response, suggest that any true association between preconception CT radiation and stillbirth is weak. Further research with detailed dose assessment and indication data is warranted.