COMPARISON BETWEEN 2 METHODS OF STANDARDIZATION FOR GESTATIONAL-AGE DIFFERENCES IN FETAL NUCHAL TRANSLUCENCY MEASUREMENT IN FIRST-TRIMESTERSCREENING FOR TRISOMY-21

Our purpose was to compare two different methods of expressing nuchal translucency (NT) measurements in first trimester screening for trisom y 21: the difference in millimeters from the median of nuchal transluc ency (delta value: delta NT) and the multiple of the expected median ( MoM). Fetal nuchal translucency was measured in 32 fetuses with trisom y 21 and in 3180 normal fetuses at 9-13 weeks' gestation. For each fet us, the measured nuchal translucency was expressed both as a delta val ue and MoM. The effectiveness of the MoM-Gaussian vs. the delta value method in modifying the age-specific risk for trisomy 21 was compared by using both the maternal age distribution of our study population an d the age distribution of a general obstetric population. The use of t he MoM-Gaussian approach led to a reduction in the false-positive rate at a given detection rate, both in the study population (by 1.2-15.2% ) and in the general population (by 0.4-2.4%). Our results suggest tha t the use of the MoM-Gaussian method might confer a potential advantag e on the screening performance of nuchal translucency in combination w ith maternal age by decreasing the false-positive rate. Further studie s in larger unselected populations will be needed to confirm the effec tiveness of this approach.