To the Editor: The meta-analysis by Dr Smith-Bindman and colleagues1 of the ultrasonographic markers to detect fetal Down syndrome contained a number of inaccurate assumptions. The estimate of Down syndrome prevalence of 1:300 in a high-risk population is not appropriate. The prevalence is greater than 1:86 for women aged 35 years and older,2 and ranges from 1:61 to 1:85 among women with an abnormal serum triple marker screen.3 This underestimated prevalence will falsely lower the positive predictive value (PPV) of the ultrasound screen and inflate the number of normal fetuses lost per fetus diagnosed with Down syndrome.
Bahado-Singh RO, Mendilcioglu I, Copel J. Ultrasound Markers of Fetal Down Syndrome. JAMA. 2001;285(22):2856-2858. doi:10.1001/jama.285.22.2856