Prenatal ultrasonography has increased 55 percent for pregnant women, even in low-risk pregnancies

Current guidelines recommend two ultrasounds in an uncomplicated pregnancy -- one in the first trimester and one in the second to screen for fetal and genetic anomalies.

The study included almost 1.4 million singleton pregnancies between 1996 and 2006 in Ontario, Canada's most populous province. It included both low-risk and high-risk pregnancies, the latter defined by the presence of a maternal comorbidity, need for genetics counselling or a prior complicated pregnancy. The study accounted for the recent introduction of first trimester nuchal translucency scanning.

The authors found that almost 1 in 5 of all pregnant women -- including those at low-risk of complications -- now receive 4 or more ultrasounds in the second and third trimesters.

"Our findings are consistent with a growing body of evidence suggesting that some health interventions most beneficial to high-risk individuals are frequently directed at apparently low-risk populations," write Dr. John You of McMaster University and coauthors.

Obstetricians practice in the highest medical-legal risk environment and may feel the need to reassure patients with a safe and relatively cost-effective ultrasound test.

"While the benefits of prenatal ultrasound in high-risk pregnancies may be more clear, the value of repeat ultrasounds in low-risk patients is not," write the authors. Since the detection of minor benign findings is increasingly more common with technological advances such as pregnancy ultrasound, they can cause anxiety and lead to invasive procedures such as amniocentesis. Increasing screening in low-risk women may also be contributing to increasing health care costs.

The authors conclude that more judicious use of prenatal ultrasounds in low-risk women is required, but there should be careful discussion over the best approach to balance frequency and medical need.