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A population-level observational study spanning three decades in Ontario, Canada, suggests a modest association between computed tomography (CT) imaging before conception and small increases in the risk of pregnancy loss and congenital anomalies. The analysis reviewed more than 5 million pregnancies and offers important data for clinicians, patients, and health systems weighing diagnostic benefits against theoretical radiation harms.
Study design and main findings
Researchers examined health records from 1992 to 2023 that covered 5,142,339 pregnancies, of which 3,451,968 resulted in live births. The study grouped patients by the number of CT scans received in the preconception period and compared pregnancy outcomes with those who had no CT imaging.
Key relative associations reported were:
- Pregnancy loss: +8% for one CT, +14% for two CTs, and +19% for three or more CTs, relative to no preconception CT.
- Congenital anomalies: +6% for one CT, +11% for two CTs, and +15% for three or more CTs.
These percentages are relative increases. For example, if a baseline risk of pregnancy loss is 10%, a 19% relative rise would change that absolute risk to about 11.9%.
Interpretation, confounding and dose considerations
This study is observational and identifies correlations, not proof of causation. Patients who undergo CT scans are often being evaluated for significant clinical issues—trauma, suspected malignancy, or other systemic disease—that themselves can increase pregnancy risks. Conditions such as diabetes, hypertension or tobacco use are more common in some patients receiving CT and can confound associations.
The investigators also analyzed which anatomical regions were scanned. Interestingly, the pattern of elevated risk was similar for head CTs and pelvis CTs. Since pelvic CTs deliver substantially more radiation to reproductive organs than head CTs, this finding argues against radiation dose alone explaining the association. As noted by an external biomedical engineer, similar risk increases across scan sites strengthen the possibility that underlying health status, not imaging dose, accounts for much of the signal.
Clinical implications and imaging alternatives
Careful clinical judgment remains essential. The absolute increases reported are small for an individual patient, but cumulative or repeated imaging could matter at population scale. Where clinically appropriate, clinicians should preferentially use lower‑or non‑ionizing options—ultrasonography and magnetic resonance imaging (MRI)—especially in younger patients and when diagnostic yield is comparable.
At the same time, failing to image a significant condition can carry far greater risks to maternal and fetal health than the theoretical radiation-related risk of a CT. Decisions should therefore be individualized, balancing diagnostic necessity, alternative modalities, and timing relative to planned conception. (Bethesda Naval Medical Center, Maryland, Hospital)
Research context and publication
The study adds to a body of literature that examines long-term population effects of medical imaging radiation. It was published in the Annals of Internal Medicine and reinforces prior calls to limit unnecessary CT use while recognizing its critical role in acute and diagnostic care.
Expert Insight
Dr. Lena Morales, fictional maternal-fetal medicine specialist: "This large administrative-data study raises important questions for public health policy and clinical practice, but it should not deter necessary imaging. For individual patients, the priority is to diagnose and manage the condition at hand—using ultrasound or MRI when clinically equivalent and reserving CT for situations where it changes immediate management. Where CT is indicated, documenting informed discussion about benefits and risks is good practice."
Conclusion
A 30-year, province-wide analysis in Ontario found modest relative increases in pregnancy loss and congenital anomalies associated with more preconception CT scans. The absolute change for most individuals is small, and residual confounding—health conditions prompting imaging—likely contributes substantially. Clinicians should continue to minimize unnecessary CT exposure, prefer non-ionizing imaging when suitable, and prioritize diagnostic decisions that protect maternal and fetal health.
Source: sciencealert
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