The biggest increase is in CT (computed tomography) scans, which use high doses of ionizing radiation to create a detailed image of the growing baby.
The use of CT scans has quadrupled in the US, and doubled in Canada, in the last 20 years, researchers at the University of California at San Francisco have discovered.
Instead of relying just on traditional ultrasound, doctors are turning to CT scans, also called medical imaging, to rule out, or detect, a serious medical condition.
"Imaging can be helpful, but it can be over-used. Always, but especially if you're pregnant, you should ask whether it is really medically necessary to have any imaging test that involves ionizing radiation," said researcher Rebecca Smith-Bindman. A CT scan releases far higher levels of radiation than a standard X-ray, and nobody knows what damage this could have to the growing fetus.
The researchers tracked the way 3.5 million pregnancies were handled in six health systems in the US and in the Canadian state of Ontario between 1996 and 2016. In that time, 5.3 percent of the women in the US, and 3.6 percent in Ontario, had a CT scan.