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Likelihood Ratio of Down Syndrome vs Normal Karyotype with use of Humerus Length (MoM)

Humerus Length (Multiples of Median) Likelihood Ratio
0.87 3.27
0.88 2.74
0.89 2.32
0.90 1.98
0.91 1.71
0.92 1.49
0.93 1.31
0.94 1.16
0.95 1.04
0.96 0.94
0.97 0.85
0.98 0.78
0.99 0.72
1.0 0.69
1.1 0.63
1.2 0.59
1.3 0.56
1.4 0.54
1.5 0.52
1.6 0.50
1.7 0.49
1.8 0.47

Expected Median Humerus Length = -6.30134 + BPD x 0.77612

Humerus Length MoM = Measured Humerus Length/Expected Median Value of Humerus

Risk = Maternal Age Risk x Likelihood Ratio eg 1/270 x 1.49 = 1/181

*Risk may be calculated from multiple sonographic markers by multiplying the likelihood ratios by the maternal age risk eg Maternal Age Risk x Humeral MoM, Nuchal MoM, Hypoplastic 5th Digit MoM, etc

Adapted from:Bahado-Singh R, Deren O, Oz U, Tan A, Hunter D, Copel J, Mahoney MJ. An alternative for women initially declining genetic amniocentesis: Individual Down syndrome odds on the basis of maternal age and multiple ultrasonographic markers. Am J Obstet Gynecol 179:514-9, 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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