First large, multicenter study to quantify exposure to ionizing radiation during 3.5 million live births.
By Janet Byron
OAKLAND, Calif., July 24, 2019 — The use of computed tomography (CT) scans during pregnancy — which exposes mothers and fetuses to ionizing radiation — has increased significantly over 21 years in the United States and Ontario, Canada.
According to the first large, multicenter study of advanced medical imaging in pregnancy, CT scans were performed in about 0.8% of pregnancies in the United States and 0.4% in Ontario in 2016. The rates of use increased nearly fourfold in the United States and doubled in Ontario over 21 years of the study.
“Trends in medical imaging during pregnancy in the United States and Ontario, Canada, 1996-2016,” was published today in JAMA Network Open.
“This study has given us a chance to look more closely at the use of advanced imaging in pregnancy,” said Marilyn L. Kwan, PhD, co-lead author and senior research scientist in the Kaiser Permanente Northern California Division of Research. “It’s important to quantify exposure to ionizing radiation because it can cause cancer and birth defects and should be kept to a minimum, especially during pregnancy.”
Researchers with the National Cancer Institute’s Radiation-Induced Cancers study reviewed data from 6 integrated health care systems in the United States and Ontario, Canada. The study included 2.2 million women who had 3.5 million live births between 1996 and 2016. They tracked the combined use of advanced medical imaging during pregnancy, including CT scans, radiography, angiography/fluoroscopy, and nuclear medicine, which involve ionizing radiation — and magnetic resonance imaging, or MRI, which does not. Ultrasound was not included in the study.
In general, CT scans are quicker, easier, and more widely available than MRIs and other advanced imaging, but they entail a large dose of ionizing radiation, many times higher than a chest X-ray.
“Most pregnant women get routine ultrasound to monitor fetal growth, which delivers no ionizing radiation,” said co-lead author Diana L. Miglioretti, PhD, biostatistics professor at the University of California, Davis, Department of Public Health Sciences, and senior investigator with Kaiser Permanente Washington Health Research Institute. “But occasionally doctors may want to use advanced imaging to detect or rule out a serious medical condition of the expectant mother, most often pulmonary embolism, brain trauma or aneurysm, or appendicitis.”
Rates of CT scanning during pregnancy in the United States started leveling off in 2007 and have been trending downward since 2010, the study found. Meanwhile, overall rates continued to increase in Ontario, Canada, but over the study period they were 33% lower than in the United States.
Researchers with the Radiation-Induced Cancers study are now examining the radiation doses that patients are exposed to during medical imaging and identifying possible associations between imaging and the risk of childhood cancer.
“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 senior author Rebecca Smith-Bindman, MD, radiology professor at University of California, San Francisco, School of Medicine. “If advanced imaging is needed, ask your doctor if you can have another imaging test that doesn’t involve exposure to ionizing radiation, such as MRI or ultrasound.”
The National Cancer Institute (R01CA185687 and R50CA211115) supported this study. The Ontario Ministry of Health also supported the Ontario, Canada, portion.
In addition to Kwan, Miglioretti, and Smith-Bindman, co-authors were Emily C. Marlow, MPH, UC Davis; Erin J. Aiello Bowles, MPH, Kaiser Permanente Washington Health Research Institute; Sheila Weinmann, PhD, Kaiser Permanente Center for Health Research; Stephanie Y. Cheng, MSc, and Jason D. Pole, PhD, ICES; Kamala A. Deosaransingh, MPH, Lisa M. Moy, MPH, and Lawrence H. Kushi, ScD, Kaiser Permanente Northern California Division of Research; Prachi Chavan, MPH, UC San Francisco; Wesley Bolch, PhD, University of Florida, Gainesville; James R. Duncan, MD, PhD, Washington University in St. Louis; Robert T. Greenlee, PhD, Marshfield Clinic Health System; Alanna K. Rahm, PhD, Genomic Medicine Institute; and Natasha K. Stout, PhD, Harvard Medical School.