Diagnostic value of nuchal translucency thickness and facial profile ultrasonic markers for trisomy 21 syndrome in the first-trimester fetuses

Objective To retrospectively assess the diagnostic value of nuchal translucency (NT) thickness and facial profile ultrasonic markers [including frontomaxillary facial (FMF) angle, and the ratio of prenasal thickness to nasal bone length (PT/NBL)] for trisomy 21 syndrome in first-trimester fetuses. Methods Ultrasonograhic images of 35 fetuses with trisomy 21 syndrome and 70 gestational age matched normal fetuses were analyzed in first-trimester. NT, FMF angle and the PT/NBL ratio were measured retrospectively in stored images from digital database between January 2012 and December 2015. The diagnostic value of NT, FMF angle and PT/NBL ratio were compared with different combinations. Results (1) The mean NT was significantly higher in the trisomy 21 group than that in controls (t=7.401, P=0.00). The NT above 2.5mm was observed in 20 trisomy 21 fetuses (57.1%) and in 3 normal fetuses (4.3%). (2) The mean FMF angle was significantly higher in the trisomy 21 group than that in controls (t=-5.283, P=0.00). The FMF angle above the 95th percentile (93.6°) was observed in 13 trisomy 21 fetuses (37.1%) and in 1 normal fetus (1.4%). (3) The mean PT/NBL ratio was significantly higher in the trisomy 21 group than that in controls (t=-7.826, P=0.00). The PT/NBL ratio above the 95th percentile (0.93) was observed in 19 trisomy 21 fetuses (54.3%) and in 4 normal fetuses (5.7%). (4) The sensitivity and Youden index for trisomy 21 increased gradually, which were 57.1% and 0.528 by using NT, and 74.3% and 0.686 by using NT and FMF angle, and 91.4% and 0.828 by using NT, FMF angle and PT/NBL ratio. There were significant differences in the detection rates of trisomy 21 among the three strategies, while the diagnostic specificity of the three strategies were more than 90%. Conclusions The three parameters are significantly increased in trisomy 21 fetus in first-trimester. First, increased NT was most commonly detected, followed by increased PT/NBL ratio, and increased FMF angle again. Detection rates for trisomy 21 fetuses in first-trimester by ultrasound screening can be significantly improved if combination of all three parameters rather than just one parameter are performed. Key words: Ultrasonography, prental; Pregnancy trimester, first; Trisomy 21; Nuchal translucency thickness; Facial profile