A large study of more than 5 million women over 30 years has suggested that CT scans before conception could increase the risk of pregnancy loss and congenital anomalies.

As concerning as the results seem, there are a lot of caveats to consider.

This observational study was conducted in Ontario, Canada, between 1992 and 2023, involving 5,142,339 pregnancies that resulted in 3,451,968 live births. Generally, rates of spontaneous pregnancy loss and congenital anomalies were found to increase in patients who had more CT scans prior to conception.

Compared to patients who had no CT scans, the risk of pregnancy loss increased by 8 percent for those who had 1 scan, 14 percent for 2 scans, and 19 percent for 3 or more scans. The risk of congenital anomalies increased by 6 percent for 1 scan, 11 percent for 2 scans, and 15 percent for 3 or more scans.

That sounds alarming, but extra context is important.

First, the increase itself is rather small: If, for example, your baseline risk is 10 percent, and it increases by 19 percent after 3 scans, the new risk is 11.9 percent.

Secondly, the study shows a correlation but not necessarily causation, and other factors are almost certainly at play. For instance, people don't tend to require CT scans for trivial reasons – the reason they're getting checked out could be a bigger driver of problems than the scan itself.