Exposure to computed tomography before pregnancy and risk for pregnancy loss and congenital anomalies: a population-based cohort study

Background — Animal studies show ovarian follicle damage and mutagenesis after ionizing radiation exposure. Computed tomography (CT) imaging is commonly done outside pregnancy, but risks to future pregnancy are unknown.

Objective — To evaluate the risk for spontaneous pregnancy loss and congenital anomalies in offspring of women exposed to CT ionizing radiation before conception.

Design — Population-based observational study.

Setting — Ontario, Canada.

Participants — 5 142 339 recognized pregnancies and 3 451 968 live births identified between 1992 and 2023.

Measurements — The exposure was the cumulative number of CT scans up to 4 weeks before conception. Outcomes were spontaneous pregnancy loss (miscarriage, ectopic pregnancy, or stillbirth) among recognized pregnancies and congenital anomalies diagnosed within the first year of life among live births.

Results — Mean maternal age was 29 years. Diabetes, hypertension, obesity, and smoking were more common in those exposed to CT imaging. Among recognized pregnancies, rates of spontaneous pregnancy loss were 101, 117, 130, and 142 per 1000 pregnancies with 0, 1, 2, and 3 or more preconception CT scans, respectively, and adjusted hazard ratios (aHRs) were 1.08 (95% CI, 1.07 to 1.08) for 1 CT scan, 1.14 (CI, 1.12 to 1.16) for 2 CT scans, and 1.19 (CI, 1.16 to 1.21) for 3 or more CT scans. Among live births, rates of congenital anomalies were 62, 84, 96, and 105 per 1000 births in those with 0, 1, 2, and 3 or more CT scans, and aHRs were 1.06 (CI, 1.05 to 1.08) for 1 CT scan, 1.11 (CI, 1.09 to 1.14) for 2 CT scans, and 1.15 (CI, 1.11 to 1.18) for 3 or more CT scans. The risk observed with head CT was not consistently lower than with CT of the abdomen, pelvis, or lower spine.

Limitation — Incomplete ascertainment of CT exposure and underlying indication may have contributed to residual confounding.

Conclusion — Exposure to preconception CT imaging may be associated with higher risks for spontaneous pregnancy loss and congenital anomalies, but causal mechanisms remain to be elucidated. Alternative imaging methods should be considered when appropriate.