The article “Proliferation of prenatal ultrasonography” 1 is commendable as an attempt to define current trends in prenatal ultrasonography. However, a population-based study has an inherent weakness, i.e. completeness of case ascertainment, potentially resulting in incorrect assignment of cases to the wrong study group. In this study, patients were “high risk” if they met one of four criteria. All others were “low risk.” This strategy would result in incorrect assignment of a major proportion of high-risk pregnancies to the low-risk group. Although it is possible that more low-risk women are having repeated scans today compared to 10 years ago, it is quite likely that this study has significantly overestimated this problem due to the weakness in study design as discussed above thereby failing to include all the high risk pregnancies in the high risk group.
Footnotes
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For the full letter, go to: www.cmaj.ca/cgi/eletters/cmaj.090979v1#263941
REFERENCE
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