In a health care system with universal access to prenatal services, we observed a 55% relative increase (adjusted) in the use of outpatient obstetric ultrasonography among singleton pregnancies over the decade from 1996/97 to 2006/07. This change was statistically significant and robust across subgroups, regardless of pregnancy risk, maternal demographic characteristics or maternal comorbidities. By 2006, over one-third of women with a singleton pregnancy were undergoing three or more outpatient ultrasound examinations during 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. This “treatment–risk paradox” has been described for statin therapy in high-risk elderly patients,11
for pharmacotherapy in patients with congestive heart failure12
and for temporal trends in the utilization of non-invasive cardiac testing.13
Although the use of prenatal ultrasonography among women with low-risk pregnancies may not account for a large proportion of total expenditures for medical imaging, it serves as a test case of a rapidly proliferating diagnostic technology. As such, it is a microcosm of a much bigger phenomenon that may be occurring with many other diagnostic imaging tests and that, cumulatively, may account for billions of dollars of health care expenditures.1,2
Others have documented substantial regional differences in utilization of obstetric ultrasonography and evidence of inappropriate use of this technology.5,18–20
In our study, rising utilization could not be explained solely by increases in maternal age, changes in maternal risk profiles or increases in uptake of first-trimester scanning for nuchal translucency. Hence, it would appear that nonclinical factors may largely explain the increases in prenatal ultrasonography that we observed. These factors may include the practice of defensive medicine, the desire to reassure a patient that her pregnancy is progressing normally, patient demand and even the “entertainment” value of seeing one’s fetus.21–24
Although the benefits of prenatal ultrasonography in high-risk pregnancies may be clearer, the value of repeat ultrasonography in low-risk patients is not.25,26
Prenatal ultrasonography is widely regarded as safe.27
However, some studies have suggested that frequent prenatal ultrasonography may be associated with intrauterine growth restriction, delayed speech and non–right-handedness.28–31
Moreover, when a prenatal ultrasound examination is performed in a low-risk pregnancy, unintended harmful consequences may outweigh any potential benefits. For example, incidental benign findings — which are becoming increasingly prevalent with advances in technology —can cause anxiety and can lead to additional investigations, some of which may be invasive, such as amniocentesis.32
More than one-third of women now undergo three or more ultrasound examinations during the second and third trimesters of a singleton pregnancy, a rate that appears to be climbing for reasons unrelated to changes in maternal risk. As such, there is a need for patients, clinicians and policy-makers to carefully consider the optimal number of obstetric ultrasound examinations per pregnancy. Assuming an average cost of $64 per examination (based on the 2008 fee schedule in Ontario33
), we estimate that the cumulative amount in fees for additional prenatal ultrasound examinations performed since 1996 was $30 million. Given the high aggregate costs of prenatal ultrasonography (because pregnancy is so common) and the evidence of potential overuse in populations not at high risk, health policy-makers could make a legitimate argument that costs be contained in groups for whom there is no documented benefit. Indeed, after the first trimester, most current guidelines recommend only a single second-trimester anatomic ultrasound examination during a pregnancy without complications.6,7
However, obstetricians function in the highest-risk medico-legal environment, where the implicit rules governing practice may differ from those in other domains of medicine, including the need to reassure patients through safe and relatively inexpensive tests like ultrasonography.21,22
In publicly funded health systems, citizens are key stakeholders in this debate, and efforts to engage citizens in deliberations about setting health care priorities should be encouraged.34
Various options for optimizing the use of obstetric ultrasonography, such as preauthorization of claims and changes to the fee schedule, will require debate and will necessarily demand a balance between policy pragmatism and an honest acknowledgement of defensive practice styles among individual providers.
Our study has some limitations. First, we had to estimate the trimester in which ultrasonography had been performed. Therefore, for preterm deliveries, some examinations actually completed in the first or second trimester would have been ascribed to a later period in the pregnancy, which would have led us to underestimate the number of first-trimester examinations. To counter this effect, we excluded multifetal pregnancies and adjusted for maternal risk, each of which is more likely to result in preterm delivery. Second, we excluded women who aborted before 20 weeks’ gestation, some of whom might have been considered to be at high risk. The remaining women in our study cohort whose pregnancies were defined as “high-risk” might have had a lower disease burden than the entire population of women with high-risk pregnancies, which might have limited somewhat the generalizability of our findings to pregnancies extending beyond 20 weeks’ gestation. Third, we did not have data about trends in the locations where the prenatal ultrasound examinations were performed, such as private physicians’ offices versus hospital-based facilities. Future studies will be needed to examine potential system-level reasons for the trends we observed. Finally, since the Ontario Health Insurance Plan database does not provide the indications for prenatal ultrasonography, we could not directly assess the appropriateness of the patterns of use that we observed. A detailed chart review, combined with surveys or interviews of mothers and their pregnancy caregivers, might better elucidate the underlying reasons for the rising use of prenatal ultrasonography.
In conclusion, there has been a substantial increase in the use of prenatal ultrasonography in the past decade, and more than one-third of women with a singleton pregnancy now receive three or more ultrasound examinations during the second and third trimesters. Efforts to promote more appropriate use of prenatal ultrasonography in low-risk groups appear warranted, but careful debate will be required to determine the most effective and acceptable approaches to achieve this goal.