Proliferation of prenatal ultrasonography.

BACKGROUND The extent to which temporal increases in the use of prenatal ultrasonography reflect changes in maternal risk is unknown. In this population-based study, we examined the use of prenatal ultrasonography from 1996 to 2006 in Ontario. METHODS With fiscal year 1996/97 as the baseline, we evaluated the relative risk (RR) and 95% confidence interval (CI) for the change in rates of ultrasonography for each subsequent year. The RR was adjusted for maternal age, income, rural residence, maternal comorbidities, receipt of genetics consultation or amniocentesis--all in the index pregnancy--and history of complications in a prior pregnancy. RESULTS The study sample consisted of 1 399 389 singleton deliveries. The rate of prenatal ultrasonography increased from 2055 per 1000 pregnancies in 1996 to 3264 per 1000 in 2006 (adjusted RR 1.55, 95% CI 1.54-1.55). The rate increased among both 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 pregnancies with at least four ultrasound examinations in the second or third trimesters rose from 6.4% in 1996 to 18.7% in 2006 (adjusted RR 2.68, 95% CI 2.61-2.74). Paradoxically, this increase was more pronounced among low-risk pregnancies (adjusted RR 2.92, 95% CI 2.83-3.01) than among high-risk pregnancies (adjusted RR 2.25, 95% CI 2.16-2.35). INTERPRETATION Substantial increases in the use of prenatal ultrasonography over the past decade do not appear to reflect changes in maternal risk. Nearly one in five women now undergo four or more ultrasound examinations during the second and third trimesters. Efforts to promote more appropriate use of prenatal ultrasonography for singleton pregnancies appear warranted.