MoM versus Delta NT: Trisomy-21 risk assessment using nuchal translucency (NT) sonography

Abstract

TRANSLUCENCY (NT) SONOGRAPHY FERGAL D. MALONE, HOWARD CUCKLE, ROBERT H. BALL, DAVID A. NYBERG, CHRISTINE H. COMSTOCK, RADEK BUKOWSKI, KEITH EDDLEMAN, SUSAN J. GROSS, LORRAINE DUGOFF, SABRINA D. CRAIGO, ILAN E. TIMOR, STEPHEN R. CARR, HONOR M. WOLFE, KIMBERLY A. DUKES, MARY E. D’ALTON, Royal College of Surgeons in Ireland, Dublin, Ireland, University of Leeds, Leeds, United Kingdom, University of Utah, Salt Lake City, Utah, Swedish Medical Center, Seattle, Washington, William Beaumont Hospital, Royal Oak, Michigan, University of Texas Medical Branch at Galveston, Galveston, Texas, Mount Sinai School of Medicine, New York, New York, Albert Einstein College of Medicine, Bronx, New York, University of Colorado Health Sciences Center, Denver, Colorado, Tufts University, Boston, Massachusetts, NYU Medical Center, New York, New York, Brown University, Providence, Rhode Island, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, DMSTAT, Boston, Massachusetts, Columbia University, New York, New York OBJECTIVE: To compare the two most commonly used approaches for interpretation of nuchal translucency (NT) sonography for Trisomy-21 risk assessment: multiples of the median (MoM) and Delta NT (NT). STUDY DESIGN: 35,087 patients had NT at 11-13 wks, including 116 cases of Trisomy-21. NT measurements were converted to both MoM and NT. NT MoMs were used with Gaussian likelihood ratios (LRs), and NTs were used with empirical LRs from a large prospective study (Spencer et al, Ultrasound Obstet Gynecol, 2003;22:142), to generate individualized patient risk estimates for Trisomy-21. A 1:270 mid-trimester risk cut-off was used to define screen positivity. RESULTS: NT distribution in unaffected pregnancies was not constant, with inter-tertile ranges of 0.67, 0.75 and 0.83 mm at 11, 12 and 13 wks respectively. The sensitivity of NT with maternal age using NT and empirical LRs was 66% (3.1% FPR), compared with 78% (8.2% FPR) when using NT MoM and Gaussian LRs. At a fixed 5% FPR, detection rates were 71% and 72% respectively. The observed prevalence of Trisomy-21 was closer to that expected from NT MoM-based risks than with the NT approach (see Table). CONCLUSION: Calculating individualized patient risk for Trisomy-21 using NT MoMs is superior to use of NT, with more cases detected, and more accurate risk estimates. (NIH-RO1-HD-38652)