CT is associated with a modest increased risk for spontaneous pregnancy loss and congenital abnormalities, according to new research published in Annals of Internal Medicine.

In a retrospective observational study, women who underwent CT once up to 1 month before conception had an 8% higher risk for miscarriage, ectopic pregnancy, or stillbirth than those who did not undergo CT. The figure rose to 14% with two screenings and to 19% with three or more screenings over the same timeframe. 

The study findings “reinforce the importance of minimizing unnecessary radiation exposure, particularly in women planning pregnancy, considering alternative imaging modalities such as ultrasounds and MRIs when appropriate, and upholding rigorous justification protocols for imaging in reproductive-age patients,” said Dushyant Sahani, MD, professor and chair of the Department of Radiology at the University of Washington School of Medicine, Seattle, who was not involved in the study. “These findings are notable, especially in light of longstanding concerns about ionizing radiation and reproductive health.” 

Researchers analyzed data from more than 5 million pregnancies and 3.5 million live births between 1992 and 2023 in Ontario, Canada. Of these, 687,692 had a CT. The median time when women underwent CT was 4 years prior to their conception date. Women were aged 16-45 years (mean age, 29). 

The risk for spontaneous pregnancy loss increased the closer the CT occurred to conception: Those who underwent CT 1-2 months before conception had a 24% higher risk than those who did not. Women in whom CT was performed near the abdomen, pelvis, or lower spine had a slightly higher risk than those screened near their heads. 

CT exposure increased the risk for congenital abnormalities within the first year of life by 6% with one screening, 11% with two screenings, and 15% with three or more screenings. Risks were similar between those who received CT of their abdomen region and of the head, suggesting that the tests may not be the only factor leading to the abnormalities, the researchers said. 

The researchers found that women who underwent CT were more likely to have a comorbidity, including endometriosis (2% vs 9%), pelvic inflammatory disease (2.0% vs 1.4%), thyroid disorders (6.1% vs 4.4%), and hypertension (3.7% vs 1.6%). 

“The concern is that inherently patients who have had CT scans and those who haven’t are different in some ways that we can measure and some ways that aren’t measurable,” said Camille Simard, MD, MSc, assistant professor of medicine in the Division of General Internal Medicine at Jewish General Hospital in Montreal, Quebec, Canada, and lead author of the study. But the findings “lead us to think that there’s potentially an association between CT scan before pregnancy and spontaneous pregnancy loss and congenital anomaly.” 

But Simard said she and her colleagues are “in no way suggesting” that clinicians avoid using CT when indicated. 

Amir A. Borhani, MD, associate professor of radiology and surgery at the Northwestern University Feinberg School of Medicine, Chicago, who was not involved in the study, said the research should remind clinicians to be more judicious when deciding to order a CT. 

“Some of the clinicians out there are way too comfortable with ordering a CT scan; many times, it’s not really indicated,” Borhani said. “I think there is a new culture of ordering CT scans just to cover everything in terms of liability or to look for rare things.” 

This study was funded by Canadian Institutes of Health Research, the Canadian Venous Thromboembolism Research Network, the Ontario Ministry of Health, and the Ministry of Long-Term Care. Simard, Borhani, and Sahani reported having no disclosures. 

Brittany Vargas is a journalist covering medicine, mental health, and wellness.