Report from ARRS: Obesity impairs obstetric sonography

Canadian researchers have found that pregnant women who are overweight or obese are more than 10 times more likely than women of normal weight to have their second trimester fetal ultrasound screening recalled due to poor results. Worse yet, a second exam may not improve visualization but instead add only to cost and patient distress.

The World Health Organization has called obesity a global pandemic. About 15% of the world's population and roughly 66% of the U.S. population is either overweight or obese. About 20% of women of reproductive age in the U.S. fit this category, according to the Centers for Disease Control and Prevention.

Obesity is considered a clinical risk factor in obstetric practice that poses a particular challenge for the completion of the second trimester fetal ultrasound survey, said principal investigator Dr. Phyllis Glanc, an assistant professor of medical imaging at the University of Toronto.

"This is a hot-button topic, but we don't believe it has been well documented," she said.

Glanc and colleagues at the university's Sunnybrook Health Sciences Center retrospectively reviewed records from 100 consecutive women with a body mass index (BMI) ≥30 when they underwent a routine second trimester fetal anatomic survey. They matched each case with two pregnant women of normal weight (BMI 20 to 25) and similar gestational age as controls. Each obese woman and her corresponding matching control underwent scanning by the same staff and equipment within a period of four days.

The investigators found that most pregnant women with high BMI had incomplete or unsatisfactory exams and that more than one-quarter of them required additional ultrasound scans to complete their surveys. Glanc presented her group's results at the 2008 American Roentgen Ray Society meeting in Washington, DC.

Twenty-six percent of screenings in the study group (BMI ≥30) were considered incomplete and required another scan as compared with only 2.5% in the control group. Scan visibility was rated as either satisfactory, moderate, or poor in 28%, 46%, and 26%, respectively, of women in the study group. In comparison, 88.5% of scans in the control group were satisfactory, while only 8.5% and 3% of them rated as either moderate or poor, respectively. Average BMI in the study group was 35.7 (range 30 to 64.8)

The most common indications for recall were inability to visualize the fetus' heart (16%), facial profile (10%), and spine (6%) compared with heart (0.5%) and spine (1%) in controls. Almost two-thirds of recalled exams remained categorized as having suboptimal visualization. Two patients scheduled for a repeat examination were lost to follow-up.

Findings highlight the challenges facing physicians responsible for managing obese pregnant patients and the need to find ways to improve their assessment, according to Glanc.

"Recall may not be the way to get around the problem of visualization," she said.

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