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Nuchal translucency thickness measurements for fetal aneuploidy screening: Log NT-MoM or Delta-NT, performer-specific medians and ultrasound training.

Research paper by Wilfried J A WJ Gyselaers, Annie J AJ Vereecken, Erik J H EJ Van Herck, Dany P L DP Straetmans, Willem U A M WU Ombelet, Jan G JG Nijhuis

Indexed on: 30 Mar '06Published on: 30 Mar '06Published in: Journal of medical screening



Abstract

To evaluate in fetal aneuploidy screening the desirability of using Fetal Medicine Foundation (FMF) normal medians of nuchal translucency thickness (NT) measurements or performer-specific medians, and whether the NT measurements should be expressed as Delta-NT or Log NT-MoM values.First trimester-combined screening programme in a low risk population in Flanders, Belgium (Algemeen Medisch Laboratorium, Antwerp).Pregnancies unaffected by trisomy 21 (T21) were screened by FMF-trained or other ultrasonographers. Performer-specific NT medians were established for FMF-trained and other ultrasonographers. NCSS Statistical Software was used to establish probability plots for Log NT-MoM and Delta-NT values, relative to performer-specific references or to the FMF-reference.A total of 16,096 pregnancies were evaluated. Six FMF-trainees and five other ultrasonographers each performed between 83 and 658 NT measurements. For the FMF-trainees, FMF-specific NT-MoM medians were close to one at a crown-rump length (CRL) between 50 and 80 mm, whereas the population-specific NT-MoM medians of the other ultrasonographers were close to one at a CRL between 40 and 80 mm. Performer-specific Delta-NT values fitted a Gaussian distribution between the 5th and 90th percentiles, while for the Log NT-MoM values this was between the 10th and 95th percentiles.We conclude that (i) the use of screening would benefit from performer-specific NT-medians based on Log NT-MoM values; (ii) the use of Log NT-MoM values is marginally better than the use of delta-NT MoMs; and (iii) NT measurements are valid at about 10 weeks (crown-rump length 40-45 mm) as well as at 11-13 weeks.