First trimester measurements of nasal bone length using three-dimensional ultrasound.

ABSTRACT

OBJECTIVES: To investigate the feasibility and reproducibility of measurements of nasal bone length using a three-dimensional (3D) ultrasound in the first trimester. METHODS: In a prospective study, 118 consecutive pregnant women attending for Down syndrome screening at 11-13 + 6 weeks were recruited. They had successful fetal nasal bone measurement by two-dimensional (2D) ultrasound by four operators. Three-dimensional volumes were recorded in the mid-sagittal plane of fetal profile by the fifth operator and examined using multiplanar techniques. Another independent investigator randomly compared his measurements with one of the four operators. RESULTS: In the subsequent 3D examination, the nasal bone length could be examined in 94 cases (79.7%). The mean difference between the 2D and 3D measurements was 0.19 mm [95% confidence interval (CI) 0.08 to 0.31] (P < 0.05). Limits of agreement were -0.73 to 1.11. The mean differences between these two observers were 0.66 mm (95% CI -0.47 to 0.86) (P < 0.05). CONCLUSIONS: There was significant intermethod difference between the results obtained by 2D and 3D, as well as substantial interobserver variation in 3D measurement of fetal nasal bone length in the first trimester. Independent 3D measurement of nasal bone offers no additional advantages over 2D sonography.