Correlation between nuchal translucency and nuchal skin-fold measurements in Down syndrome and unaffected fetuses

To assess whether there is a correlation between nuchal translucency (NT) and nuchal skin-fold (NF) measurements, in Down syndrome and in normal pregnancies.

Nineteen Down syndrome and 224 normal fetuses underwent ultrasound sequential examinations at 11-13 weeks and 14-28 weeks' gestation. NT was measured at the earlier examination and NF at the later one. Both markers were expressed in multiples of the normal gestation-specific median (MoM). The affected cases had been referred to us for termination of pregnancy; NT had been measured locally and NF was measured at our center prior to the procedure. All unaffected pregnancies were scanned routinely at our center.

There was no statistically significant correlation between NT and NF, in either the Down syndrome (r = 0.076, P = 0.76) or the unaffected (r = - 0.021, P = 0.76) pregnancies. The median NF value in Down syndrome fetuses was 1.538 MoM, compared with 0.990 in unaffected fetuses (P < 0.0001). Gaussian modeling with parameters from a published meta-analysis, updated to include the current series, predicted a 91% detection rate of Down syndrome for a 5% false-positive rate when NF replaced second-trimester biochemistry in a sequential contingent screening strategy.

While this study cannot exclude a small correlation between NT and NF, and the Down syndrome karyotype was known at the time of the NF scan, the markers can be considered as independent determinants of Down syndrome risk. Modeling suggests that sequential contingent screening incorporating NF is an effective screening strategy, although this needs to be confirmed in a prospective study.