A large Canadian study involving more than five million women over three decades suggests that CT scans before conception may slightly increase the risk of pregnancy loss and congenital anomalies.
The research, published in the Annals of Internal Medicine, analyzed pregnancies in Ontario, Canada, between 1992 and 2023. It found that women who underwent CT scans before becoming pregnant faced modestly higher risks of complications compared with those who had no scans.
What the study found
Researchers looked at 5,142,339 pregnancies resulting in 3,451,968 live births. They observed a dose-response pattern. The more CT scans a woman had before conception, the higher the risk of adverse outcomes.
Compared with women who had no CT scans:
- One CT scan was linked to an 8 percent higher risk of pregnancy loss. It was also connected to a 6 percent higher risk of congenital anomalies.
- Two scans were linked to a 14 percent higher risk of pregnancy loss. They were also linked to an 11 percent higher risk of congenital anomalies.
- Three or more scans were linked to a 19 percent higher risk of pregnancy loss and a 15 percent higher risk of congenital anomalies.
Why the results need careful interpretation
Despite the size of the study, experts caution against drawing simple conclusions. First, the relative risk increases were small. For example, if the baseline risk of pregnancy loss is 10 percent, three CT scans would increase it to approximately 11 percent.
Second, the study shows correlation rather than causation. Health conditions prompting a CT scan may themselves contribute to higher pregnancy risks. “Women who undergo CT scans were more likely to have health conditions like diabetes, hypertension, or smoking. These conditions themselves raise pregnancy risks,” explained Dr. Alex Polyakov, a gynecologist at the University of Melbourne, who was not involved in the research.
Radiation dose may not be the main factor
Interestingly, the researchers found that the type of CT scan did not significantly alter the risk pattern. “They find that the increased risk resulting from a head CT scan is pretty similar to the increased risk from a pelvis CT scan,” noted Derek Hill, a biomedical engineer. Derek Hill is a biomedical engineer at University College London.
Head scans expose the reproductive organs to far less radiation than pelvic scans. This raises doubts about whether radiation exposure is the main driver of the risks. Instead, underlying health issues may play a larger role.
Practical implications for patients and doctors
The study supports existing medical advice: avoid unnecessary CT scans in younger patients and women of reproductive age when safer alternatives exist. “Although the increase in risk is small for any one patient, it’s worth prioritizing less harmful alternatives if they can provide similar outcomes,” the study concludes.
Techniques such as ultrasound or magnetic resonance imaging are already recommended as first-line options in many diagnostic cases. Experts stress that failing to diagnose a serious condition could pose far greater risks. These risks outweigh the small increases linked to pre-pregnancy CT scans. Decisions should be based on individual health needs and weighed carefully by healthcare providers.
This landmark study offers new evidence that CT scans before conception may slightly raise the risks of pregnancy loss and birth defects. However, the findings highlight the importance of context, since many women requiring scans already face higher health risks.
For most patients, the takeaway is not to avoid medically necessary CT scans, but to ensure they are used judiciously, with alternatives considered where appropriate.
