Effects of period of gestation and position of fetal neck on nuchal translucency measurement.

OBJECTIVE The aim of this study was to determine the effects of period of gestation and position of fetal neck on nuchal translucency measurement. MATERIALS AND METHODS Nuchal translucency was measured in the mid-sagittal plane, with the fetal neck in the flexed, neutral, and extended positions in 100 pregnant women between 11 and 13(+6) weeks. Mean nuchal translucency measurements at different periods of gestation were compared. Differences between the extended and neutral positions (Δ extended nuchal translucency) and those between the flexed and neutral positions (Δ flexed nuchal translucency) were calculated. The repeatability coefficients for the measurements in all the three positions were computed. Statistical analysis was also done. RESULTS Nuchal translucency values were 1.050 ± 0.282 mm in the 11th week, 1.243 ± 0.348 mm in the 12th week, and 1.823 ± 0.357 mm in the 13th week (r = 0.747, p < 0.0001). The mean Δ flexed value was 0.233 ± 0.133 mm lesser than the neutral value (p < 0.0001). The mean Δ extended nuchal translucency was 0.305 ± 0.155 mm greater than the neutral value (p < 0.0001). The repeatability coefficient was the lowest in the neutral position (0.17 mm in the neutral position, 0.28 in the flexed position and 0.41 mm in the extended position). CONCLUSION We concluded that the period of gestation and fetal neck position can make a significant difference to nuchal translucency measurement. Repeatability of measurement is more accurate with the fetal neck in the neutral position. These findings have important implications for clinicians using nuchal translucency to screen the obstetric population for Down's syndrome.