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Ultrasound Criteria and Likelihood Ratios Assigned for Detection of Trisomy 21


Sonographic Finding


Likelihood Ratio Assigned

Structural Defect

cardiac defect, cystic hygroma with or without hydrops, cerebral ventricular dilatation


Nuchal Thickening

> 5 mm in the antero-posterior plane


Echogenic Bowel

subjectively increased, grades 2 or 3


Short Humerus

observed/predicted ratio <= 0.89


Short Femur

observed/predicted ratio <= 0.91


Echogenic Intracardiac Focus

present or absent


Renal Pyelectasis

> 3 mm in the antero-posterior plane


Normal Ultrasound Scan

none of the above


Likelihood ratio for each ultrasound marker is defined as: sensitivity / false-positive rate as an isolated finding.

Asterisk indicates likelihood ratios assigned from data of Snijders RJM, Nicolaides KH. Ultrasound Markers for Fetal Chromosomal Defects. Carnforth, UK: Parthenon Publishing, 1996. Remaining data from Nyberg et al's institution.

From: Nyberg DA, Luthy DA, Resta RG, Nyberg BC, Williams MA. Age-adjusted ultrasound risk assessment for fetal Down's syndrome during the second trimester: description of the method and analysis of 142 cases. Ultrasound Obstet Gynecol 12:8-14, 1998.

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Ultrasound Educational Press     Go Top
Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California

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