The effect of ethnic origin on nuchal translucency at 10-14 weeks of gestation

Fetal nuchal translucency (NT) increases with gestation and is affected by fetal posture and fetal gender. A recent report suggested that there might also be ethnic differences. We investigated the effect of ethnic origin on NT in an Asian population.

NT was measured at 10-14 weeks. The measurements were converted into multiples of the median (MoM) for gestational day. The risk of Down syndrome was calculated by combining NT and maternal age. Cases affected by chromosomal and major structural abnormalities were excluded. NT measurements of different ethnic groups were compared.

Between January 1997 and October 2001, 16 981 pregnancies with known ethnic origin and normal fetal outcome were analysed. Median NT MoM (95% CI) of the Filipinos was 1.07 (1.04-1.11). This was significantly higher than that of the Chinese, 1.01 (1.01-1.02); other Asians (Indians, Pakistanis and Nepalese), 0.96 (0.94-0.99), and Caucasians, 0.98 (0.93-1.06) (p<0.05, respectively; Mann-Whitney U-test). An NT risk cut-off of 1:180 would classify 5% of the Chinese, 4.6% of the Caucasians, 5.6% of the Filipinos and 4.2% of the other Asians as screen-positive. There were no statistically significant differences between these screen-positive rates (p>0.05, Chi-square test).

Although there were statistically significant differences in NT measurements between different ethnic groups, it was clinically insignificant, as reflected by similar screen-positive rates.