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


METHODS
First trimester-combined screening programme in a low risk population in Flanders, Belgium (Algemeen Medisch Laboratorium, Antwerp).


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Ziekenhuis Oost Limburg, Genk, Belgium. wilfried.gyselaers@zol.be
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
D000782:Aneuploidy; D025063:Chromosome Disorders / Q000175:diagnosis* / Q000000981:diagnostic imaging*; D003627:Data Interpretation, Statistical; D004314:Down Syndrome / Q000175:diagnosis / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D015233:Models, Statistical; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011336:Probability; D012984:Software; D014463:Ultrasonography; D016216:Ultrasonography, Prenatal / Q000379:methods*