The effect of fetal neck position on nuchal translucency measurement.

Objective: To determine the influence of the position of the fetal neck on nuchal translucency measurement.

Design: A prospective cross-sectional study.

Population: One hundred and ninety-six.

Methods: Nuchal translucency was measured in the mid-sagittal plane, with the fetal neck in the flexed, neutral and extended positions. Measurements were made to the nearest 0.1 mm. Statistical analysis used the paired t-test for differences between the extended and neutral positions, [delta extended nuchal translucency] and the flexed and neutral positions [delta flexed nuchal translucency].

Results: The mean extended nuchal translucency was 0.62 mm greater than the mean neutral nuchal translucency value [95% confidence interval 0.53 to 0.70, T = 14.33, P < or = 0.00001]. The mean flexed nuchal translucency was 0.40 mm less than the mean neutral nuchal translucency value [95% CI 0.34 to 0.47, T = 11.99; P = < 0.00001]. The repeatability coefficient was lower in the case of neutral nuchal translucency measurements [0.48] and was higher in the other groups [extended = 1.04, flexed = 0.70].

Conclusion: Fetal neck position can make a significant difference to nuchal translucency measurements. Repeatability of measurements are more accurate with the fetal neck in the neutral position. These findings have important implications for clinicians using nuchal translucency to screen the general obstetric population.