Comparison between two methods of standardization for gestational age differences in fetal nuchal translucency measurement in first‐trimester screening for trisomy 21

Abstract

Our purpose was to compare two different methods of expressing nuchal translucency (NT) measurements in first-trimester screening for trisomy 21: the difference in millimeters from the median of nuchal translucency (delta value: delta NT) and the multiple of the expected median (MoM). Fetal nuchal translucency was measured in 32 fetuses with trisomy 21 and in 3180 normal fetuses at 9-13 weeks' gestation. For each fetus, the measured nuchal translucency was expressed both as a delta value 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 and the age distribution of a general obstetric population. The use of the 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 that the use of the MoM-Gaussian method might confer a potential advantage on the screening performance of nuchal translucency in combination with maternal age by decreasing the false-positive rate. Further studies in larger unselected populations will be needed to confirm the effectiveness of this approach.

Correlation and Overlapping between Nuchal Translucency and Triple Test among Down Syndrome-Affected Pregnancies

“…Total congruency or high correlation between any two tests means that there is no advantage in performing both. Lack of correlation between NT and TT in normal pregnancies [14] and in cases with DS, found in the present study, validates the methodology of multiplication of the LRs [23,24] in order to obtain a meaningful integrated risk. Analysis of the extent of overlapping in our study showed that between 25 and 35 years there was an average overlapping of around 33% among the screen positive cases of DS.…”

“…The extent of overlapping between the tests was evaluated using age-adjusted calculations performed according to the methodology reported before [21][22][23]. The LRs of the tests were adjusted to specific age-derived background risks.…”

Incidence of Chromosomal Abnormalities in the Presence of Fetal Subcutaneous Oedema, Such as Nuchal Oedema, Cystic Hygroma and Non-Immune Hydrops

“…Based on studies involving a wider sample however [15,28,29] , the risk of chromosomal abnormalities was in the range of 7.49 and 9.57%. Our result was 8.3%, corresponding with these literature data.…”

“…In the first trimester, nuchal translucency (NT) is investigated, in which the distance between the external surface of the occipital bone and the internal surface of the skin is measured in a longitudinal section [6][7][8][9][10] , its proposed limit being 3 mm [11][12][13][14] . Some authors recommend the use of a multiple of median, compared to values measured at different weeks of normal pregnancies [15][16][17][18] .…”

The role of ductus venosus blood flow assessment in screening for chromosomal abnormalities at 10–16 weeks of gestation

“…Increased fetal nuchal translucency (NT) seems to be a well established ultrasonographic marker for aneuploidy screening, particularly when it is measured during the first trimester [1][2][3][4][5] . To date, NT screening combined with maternal age at early mid-trimester can identify about 75 -80% of chromosomal abnormalities with a false-positive rate of 5% 1,6 -8 .…”