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Previous CT scans may slightly increase risks of pregnancy loss and birth defects, according to a major Canadian study involving over 5 million pregnancies. The study found that women who had undergone one or more CT scans before conception showed a small but statistically significant rise in miscarriage and congenital anomalies rates. Experts stress that while the increased risks are minimal, medical imaging with radiation should be judiciously used in women of childbearing age to balance clinical benefits and potential harms.
Previous CT Scans Linked to Slightly Elevated Pregnancy Risks
A landmark population-based cohort study published in the Annals of Internal Medicine (2025) analyzed data from 5,142,339 pregnancies in Ontario, Canada, spanning 1992 to 2023. The researchers examined the association between exposure to computed tomography (CT) scans prior to conception and subsequent pregnancy outcomes, specifically spontaneous pregnancy loss (including miscarriage, ectopic pregnancy, and stillbirth) and congenital anomalies diagnosed within the first year of life.
Women who underwent one or more CT scans within months or years before conceiving were found to have an increased risk of pregnancy loss and birth defects compared to those who had not undergone CT imaging. The rate of pregnancy loss increased progressively with the number of CT scans: 117 losses per 1,000 pregnancies with one CT scan, 130 with two, and 142 with three or more, compared to 101 per 1,000 for those without prior CT scans. Similarly, congenital anomalies occurred in 84 per 1,000 births after one CT scan, rising to 105 per 1,000 with three or more CT scans, versus 62 per 1,000 in women without prior scans.
Expert Commentary and Context
Dr. Camille Simard, lead researcher from Jewish General Hospital in Montreal, emphasized that while the elevated risks correlate with the number of CT scans, the absolute increase in risk remains small. She advised clinicians to carefully consider imaging choices in younger women and to communicate clearly about the reasons for CT imaging when it is necessary.
Professor Derek Hill, an expert in medical imaging science at University College London, noted that the study highlights an association but does not prove causation. He explained that women requiring CT scans may already have health conditions increasing their pregnancy risks, not just radiation exposure from the scans. Hill also pointed to the similarity in risk elevation whether the CT scan targeted the head or pelvis, suggesting that underlying health factors may be a significant contributor.
Professor Simon Jolly from UCL stated the findings underscore the importance of prioritizing non-ionizing imaging methods such as ultrasound or MRI, particularly for women of reproductive age or those planning pregnancy. Nonetheless, he acknowledged that CT scanning remains essential when clinically indicated due to its diagnostic efficacy.
Associate Professor Alex Polyakov of the University of Melbourne explained the increase in risks, while statistically significant, might not be clinically meaningful at an individual level. He noted potential confounders such as concurrent health conditions or trauma that lead to CT scans and independently raise pregnancy risks. He also highlighted limitations inherent in registry-based studies that rely on healthcare databases.
Understanding Radiation and Pregnancy Risks
Unlike X-rays, CT scans expose patients to higher doses of ionizing radiation that can potentially damage DNA in ovarian follicles. This damage, even months or years before conception, might affect the early embryo after fertilization, raising the risk of miscarriage or congenital anomalies.
The human fetus is known to be most vulnerable to radiation between 2 and 15 weeks of gestation, a critical period when organ formation occurs. However, prenatal exposure from maternal CT imaging during pregnancy is typically kept below thresholds considered harmful for birth defects. This study focuses on pre-conception exposure, which is less understood.
Public Health and Clinical Implications
Given the widespread use of CT imaging, especially for diagnostic purposes, this study provides important evidence for clinical decision-making. It signals a need for heightened caution in ordering CT scans among women likely to conceive. Health providers are encouraged to follow established appropriateness guidelines and favor lower or non-ionizing radiation alternatives such as ultrasound or magnetic resonance imaging (MRI) when suitable.
The study also underscores the importance of patient-provider communication about the risks and benefits of imaging tests and the rationale for their use. This can help women make informed choices that consider both immediate medical needs and potential future reproductive risks.
Limitations and Balanced Perspective
Researchers stressed that the study’s observational design means it can only demonstrate associations, not causation. Confounding factors such as pre-existing health conditions that prompt CT imaging may partly explain the increased risk. Furthermore, the absolute risk increase is modest, meaning most women who had CT scans before conception will still have healthy pregnancies. The authors caution against unnecessary alarm and emphasize that clinically needed CT imaging should not be withheld.
More research is recommended to clarify underlying biological mechanisms and to examine risks in other populations. The results may inform updates to clinical guidelines on imaging use in women of reproductive age but should be interpreted carefully in context.
Medical Disclaimer
This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.
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