Proliferation of Prenatal Ultrasonography

Abstract

It has been generally recommended that a woman with an uncomplicated pregnancy receive 2 ultrasound examinations during gestation. For largely unexplained reasons, the number of such examinations performed during a single pregnancy has markedly increased. Some investigators have suggested that the increase reflects changes in maternal risk over time. However, there is no clear data showing that temporal increases in the use of prenatal ultrasound examinations are associated with increased risk. The investigators in this present study believed that elevated maternal risk was not the sole explanation for more frequent use of this imaging test, and that increased use of ultrasound examinations would also be observed among low-risk pregnancies. This repeated cross-sectional population-based study investigated the annual rates of prenatal ultrasonography in women with a singleton delivery, over an 11-year period (1996-2006) in Ontario, Canada. Several linked administrative databases were used to obtain information on obstetric deliveries and to identify maternal co-morbidities. Using fiscal year 1996/97 as the baseline, for each fiscal year between 1996 and 2007, the relative risk (RR) for the change in rates of ultrasonography for each subsequent year was calculated. Multivariate analysis was used to adjust the RR for maternal age, neighborhood income, rural residence, diabetes, hypertension or other maternal co-morbidities, genetics consultation, and amniocentesis —all in the index pregnancy—and a history of a previous pregnancy with complications. The primary study outcome was the annual rate of utilization of prenatal ultrasound examinations among low-risk and high-risk pregnancies. The study population was comprised of 1,399,389 singleton deliveries. Between 1996 and 2006, the rate of prenatal ultrasonography for any trimester rose from 2055 pregnancies per 1000 pregnancies to 3264 per 1000 pregnancies; the adjusted RR was 1.55, with a 95% confidence interval (CI) of 1.54 to 1.55. There was no difference in the extent of the increase in rates among women with low-risk pregnancies (adjusted RR = 1.54; 95% CI = 1.53-1.55) and those with high-risk pregnancies (adjusted RR = 1.55; 95% CI = 1.54-1.57). The proportion of pregnant women who received 4 or more fetal ultrasound examinations in the second or third trimester increased from 6.4% in 1996 to 18.7% in 2006; this corresponds to an adjusted RR of 2.68 (95% CI = 2.61-2.74) across the decade. The increased use of ultrasound examinations was more pronounced in low-risk pregnancies (adjusted RR = 2.92; 95% CI = 2.83-3.01) than in high-risk pregnancies (adjusted RR = 2.25; 95% CI = 2.16-2.35). These findings showed a substantial increase in the rate of prenatal ultrasonography among singleton pregnancies over an 11-year period, for reasons apparently unrelated to increased maternal risk. The need to reassure pregnant women must be balanced with efforts to promote the appropriate use of prenatal ultrasonography in low-risk groups.