OC78: The impact of tissue harmonic on the measurement of nuchal translucency thickness

Abstract

The aim of the study was to evaluate the effect of tissue harmonic imaging (THI) on the measurement of fetal nuchal translucency (NT) thickness. Some 103 pregnant women during the first trimester of pregnancy underwent measurement of nuchal translucency according to the Fetal Medicine Foundation criteria. NT was evaluated using conventional ultrasonography (CUS) and THI without changing any other parameter (e.g. gain). For each patient three images with CUS and three images with THI were stored and then measured independently by two different operators. The maximum measurements using CUS and THI were compared. For statistical analysis t-test was used. Probability values of < 0.05 were considered significant. The mean maternal age was 32.8 (range, 20–42) years. The gestational age was mean 12 + 1 (range, 11 + 0–13 + 6) weeks. The mean CRL was 55.8 mm ( ± 7.2 mm). The mean fetal NT was 1.5 mm ( ± 0.41 mm) using CUS and 1.2 mm ( ± 0.43 mm) using THI (P < 0.001). A second operator remeasured the first 50 cases: the mean fetal NT was 1.4 mm ( ± 0.47 mm) using CUS and 1.1 mm ( ± 0.4 mm) using THI (P < 0.001). Fetal NT measurements were above the median in 49 cases (47.6%) using CUS and just in 24 cases (23.3%) with THI. THI gives a significant underestimation of the NT thickness and this could reduce the sensitivity of screening for Down syndrome.