Measurement of fetal nuchal translucency thickness by three-dimensional ultrasound.

OBJECTIVE To investigate the feasibility and repeatability of nuchal translucency thickness measurement using three-dimensional ultrasound. METHODS Forty consecutive women with uncomplicated singleton pregnancies attending for Down syndrome screening at 11-14 weeks' gestation were included in this prospective crossover trial. Nuchal translucency thickness was measured using both two-dimensional and three-dimensional ultrasound. In each case two three-dimensional volumes were recorded and then examined by using the technique of planar reformatted sections. The initial plane of the first volume always contained a clear image of the nuchal region ('sagittal volume'), whilst the initial plane of the second volume was selected randomly regardless of fetal position ('random volume'). The repeatability of nuchal translucency measurement was examined by constructing a scatter diagram of the difference between the measurements plotted against the mean of two readings. RESULTS Nuchal translucency measurements could be repeated in 38/40 (95%) sagittal volumes and 24/40 (60%) random volumes. The mean difference between two-dimensional measurements and those obtained by reslicing of sagittal three-dimensional volumes was -0.097 mm (95% limits of agreement from -0.481 to 0.675) and 0.225 mm (95% limits of agreement from -0.369 to 0.819) when random volumes were examined. CONCLUSIONS Reslicing of stored three-dimensional volumes can be used to replicate nuchal translucency measurements only when nuchal skin can also be clearly seen on two-dimensional ultrasound.