Increased Pregnancy Risks linked to Prior CT Scans: A new Ontario Study
A recent population-based cohort study conducted in Ontario,examining births between 1992 and 2023 among women aged 16 to 45,has revealed a potential association between prior exposure to computed tomography (CT) scans and adverse pregnancy outcomes. The study, published in Annals of Internal Medicine on September 9, 2025 (doi:10.7326/ANNALS-24-03479), analyzed data from 687,692 pregnancies where women had undergone at least one CT scan at least one month before conception.Researchers,led by Dr. Camille Simard of McGill University and Jewish General Hospital in Montreal, found that rates of spontaneous pregnancy loss - encompassing miscarriage, ectopic pregnancy, and stillbirth – increased with the number of prior CT scans. The rate was 101 per 1,000 pregnancies for women with no prior CT scans, rising to 117, 130, and 142 per 1,000 pregnancies for those with one, two, and three or more scans, respectively. Even after adjusting for individual risk factors, the odds of pregnancy loss were 8% higher (adjusted hazard ratio [aHR] 1.08; 95% Confidence Interval [CI], 1.07-1.08) with one scan, 14% higher (aHR 1.14, 95% CI 1.12-1.16) with two scans, and 19% higher (aHR 1.19, 95% CI 1.16-1.21) with three or more scans.
The study also indicated a correlation between CT scan exposure and congenital anomalies in live births. The rate of congenital anomalies was 62 per 1,000 births among women with no prior CT scans, compared to 84, 96, and 105 per 1,000 births for those with one, two, and three or more scans, respectively.Adjusted risk increased by 6% (95% CI, 1.05-1.08) for one scan, 11% (95% CI, 1.09-1.14) for two scans, and 15% (95% CI, 1.11-1.18) for three or more scans.
Interestingly, the increased risk was not consistently lower for head CT scans compared to imaging of the abdomen, pelvis, or lower spine. Researchers hypothesize that this suggests ovarian follicles may be susceptible to damage from ionizing radiation nonetheless of the scan location, possibly leading to genetic mutations and chromosomal changes in eggs even months or years before conception. The study noted that half of the scans occurred four or more years prior to conception, yet risk still increased as the timing of imaging moved closer to conception.
The study authors emphasize the importance of adhering to appropriate imaging criteria when choosing between CT, ultrasound, and magnetic resonance imaging (MRI).they recommend careful consideration of CT use in young women and clear communication with patients regarding the benefits and risks of the procedure.
in an accompanying editorial, Dr. Seth Hardy of Penn State health highlighted that previous research suggests over one-third of diagnostic imaging studies may be unnecessary, underscoring the potential for reducing patient exposure.The authors acknowledge limitations, including the possibility of residual confounding due to underlying health conditions. Women who underwent CT scans were more likely to have pre-existing conditions like diabetes,hypertension,or smoking habits,all of which are known risk factors for adverse pregnancy outcomes. Data gaps regarding women’s lifetime CT scan exposure and other potential contributing medical problems were also noted.
While the study does not establish a causal relationship, the researchers recommend clinicians prioritize nonionizing imaging alternatives when feasible and ensure patients are fully informed about the potential benefits and risks of CT imaging.
