A large Canadian population-based cohort study has found that women exposed to computed tomography (CT) scans before conception face a slightly elevated risk of pregnancy loss and congenital anomalies, with risks rising with the number of scans and their proximity to conception.

Camille Simard, MD

Courtesy of JGH News

The study, published in Annals of Internal Medicine, analyzed 5,142,339 recognized pregnancies and 3,451,968 live births in Ontario between 1992 and 2023 among women aged 16 to 45 years. Among these pregnancies, 687,692 involved women who had undergone at least 1 CT scan at least 1 month before conceiving. Rates of spontaneous pregnancy loss, including miscarriage, ectopic pregnancy, and stillbirth, were 101 per 1,000 pregnancies among those with no prior CT scans, compared with 117, 130, and 142 per 1,000 among those with 1, 2, and 3 or more scans, respectively, according to the study. After adjusting for individual risk factors, the odds of pregnancy loss were 8% higher (aHR 1.08; 95% CI, 1.07–1.08) for 1 scan, 14% higher (1.14, 1.12–1.16) for 2, and 19% higher (1.19, 1.16–1.21) for 3 or more scans.

Researchers, led by Camille Simard, MD, assistant professor at McGill University and an internist in the Obstetric Medicine Clinic at Jewish General Hospital in Montreal, reported a similar trend for congenital anomalies. Among live births, rates of congenital anomalies were 62 per 1,000 births in those with no previous CT scans, compared with 84, 96, and 105 per 1,000 for mothers with 1, 2, and 3 or more scans, respectively, for an adjusted increased risk of 6% (CI, 1.05–1.08), 11% (CI, 1.09–1.14), and 15% (CI, 1.11–1.18) for 1, 2 and 3 or more scans.

The investigators found that the risk was not consistently lower for head CT compared with imaging of the abdomen, pelvis, or lower spine, suggesting that ovarian follicles “may be vulnerable to damage from ionizing radiation at any point, including many months or years before conception,” resulting in genetic mutations and chromosomal changes in the unfertilized egg that might have consequences after fertilization. Half of the scans occurred 4 or more years before conception, yet risk increased as imaging occurred closer to conception.

Simard and colleagues emphasized the importance of appropriate imaging choices: “Follow appropriateness criteria when deciding between CT, ultrasound and magnetic resonance imaging, be thoughtful about CT use in young women, and communicate clearly with patients why CT is the best option for their specific case.”

The findings highlight a potential mechanism for the association. The authors noted that ovarian follicles may sustain radiation-induced genetic mutations or chromosomal damage months or even years before fertilization, with consequences for early embryonic development.

In an editorial accompanying the study, Seth Hardy, MD, associate professor in the department of radiology at Penn State Health, in Hershey, PA, wrote that previous studies suggest that more than one-third of diagnostic imaging studies may not be necessary. “The implications of this work are profound,” Hardy wrote.

Among the study’s limitations the authors acknowledge that underlying conditions may have contributed to residual confounding of the findings. Women who had CT scans were more likely to have health conditions, including diabetes, hypertension, or smoking, all of which raise the risk for poor pregnancy outcomes. Sinard et al also noted that there were gaps in data on women’s lifetime exposure to CT scans and that other underlying medical problems could contribute to their birth outcomes.

Although the study cannot prove causation, the authors recommend that clinicians consider nonionizing imaging alternatives when appropriate and ensure clear communication with patients regarding the benefits and risks of CT imaging.

References

Sinard C, Fu L, Odugbemi T, et al. Exposure to computed tomography before pregnancy and risk for pregnancy loss and congenital anomalies: A population-based cohort study. Ann Intern Med. Published online September 9, 2025. doi:10.7326/ANNALS-24-03479