Effect of deviation of nuchal translucency measurements on the performance of screening for trisomy 21
Article first published online: 30 APR 2009
Copyright © 2009 ISUOG. Published by John Wiley & Sons, Ltd.
Ultrasound in Obstetrics & Gynecology
Volume 33, Issue 6, pages 657–664, June 2009
How to Cite
Kagan, K. O., Wright, D., Etchegaray, A., Zhou, Y. and Nicolaides, K. H. (2009), Effect of deviation of nuchal translucency measurements on the performance of screening for trisomy 21. Ultrasound Obstet Gynecol, 33: 657–664. doi: 10.1002/uog.6370
- Issue published online: 28 MAY 2009
- Article first published online: 30 APR 2009
- Manuscript Accepted: 6 MAR 2009
- Fetal Medicine Foundation. Grant Number: 1037116
- first trimester;
- nuchal translucency;
- quality assurance;
- trisomy 21
To examine the effect of deviations in median nuchal translucency thickness (NT) and the spread in measurements on the performance of screening for trisomy 21 by maternal age and fetal NT, and by maternal age, fetal NT and maternal serum biochemistry.
We simulated the NT and multiples of the median values for pregnancy-associated plasma protein-A (PAPP-A) and free β-human chorionic gonadotropin (β-hCG) for 500 000 euploid and 500 000 trisomy 21 pregnancies at 12 weeks of gestation. Detection rates for trisomy 21 and false-positive rates were calculated without adjustments in NT and by adding or subtracting values ranging from 0.1 to 1.0 mm to each observed measurement. In addition, the effects of variation in the scatter of NT measurements were examined by applying a multiplicative factor ranging from 0.5 to 2 to the SD.
The detection rate of trisomy 21 for a fixed false-positive rate of 3% in screening by maternal age and fetal NT was 72%, and in screening by maternal age, fetal NT and serum free β-hCG and PAPP-A it was 86%. A consistent underestimate or overestimate in the measured NT reduced the detection rate of trisomy 21 for a fixed-false positive rate. At a fixed screen-positive cut-off an underestimate in fetal NT reduced the detection rate whereas an overestimate in NT increased the false-positive rate. A widening in the scatter of measurements had only a small impact on the detection rate but it caused a major increase in the false-positive rate.
High performance of screening necessitates appropriate measurement of fetal NT. This paper demonstrates the effect of deviations in the median and SD of NT from the expected on the performance of screening and can form the basis of audit of results of individual sonographers. Copyright © 2009 ISUOG. Published by John Wiley & Sons, Ltd.