Figure 1.

Relative risk (RR) of undergoing obstetric ultrasonography from fiscal year 1996/97 to fiscal year 2006/07. Increases in the annual rate of prenatal ultrasonography are expressed as relative risk, with fiscal year 1996/97 as the referent. Data were adjusted for maternal age, income quintile, rural versus urban place of residence, any diabetes mellitus, any hypertension, any other maternal comorbidity, genetics consultation and amniocentesis — all in the index pregnancy — and a history of complications in a prior pregnancy. For all trends, p < 0.001. CI = confidence interval.