Abdominopelvic computed tomography during pregnancy and the risk of congenital malformations: protocol for a nationwide population-based cohort study in South Korea

INTRODUCTION: The use of CT has increased markedly over recent decades, and this trend is also observed among pregnant women. According to current clinical guidelines, fetal radiation exposure below a threshold of 100 to 200 mGy does not appear to increase the risk of congenital malformations. Although the estimated fetal dose from a maternal abdominopelvic CT examination is generally lower than this range, evidence regarding the risks associated with such relatively low-dose diagnostic exposures during pregnancy remains scarce. This study aims to evaluate the association between abdominopelvic CT exposure during the first trimester of pregnancy and the risk of congenital malformations in infants. METHODS AND ANALYSIS: We will conduct a nationwide population-based cohort study using the National Health Insurance Service (NHIS) database of South Korea. All live births from 2011 through 2023 will be identified and linked to their mothers. Exposure will be defined as maternal abdominopelvic CT during the first trimester of pregnancy. The primary outcome is major congenital malformations in infants, defined according to the standardised classification system of the European Surveillance of Congenital Anomalies. Secondary outcomes include organ-specific malformations and congenital malformations requiring neonatal intensive care unit admission or corrective surgery. A propensity score-based fine stratification weighting approach will be used to adjust for covariates as potential confounders, and relative risks will be estimated. Prespecified sensitivity analyses will be conducted to assess robustness of the findings. ETHICS AND DISSEMINATION: This study has been approved by the Institutional Review Board of Seoul National University Bundang Hospital (Institutional Review Board No. X-2508-993-902). Informed consent was waived because only anonymised administrative claims data will be used. All analyses will be conducted within the secure NHIS research environment, and no individually identifiable data will be released. The study findings will be disseminated through peer-reviewed publications, scientific conference presentations and communication with regulatory authorities, clinicians and policymakers.