Screening for Down's syndrome by fetal nuchal translucency measurement in a high-risk population

Objective. To examine the discriminative capacity of nuchal translucency measurement in the detection of trisomy 21 and other chromosomal anomalies. Design. Prospective cohort study. Subjects. A total of 2247 women with viable singleton pregnancies between 10 and 14 weeks' gestation attending a prenatal diagnosis center for fetal karyotyping. Methods. The fetal nuchal translucency was measured transabdominally in all women before invasive prenatal testing. Results. Chromosomal abnormalities were found in 63 fetuses, including 36 with Down's syndrome. The likelihood of the presence of chromosomal abnormalities increased with larger nuchal translucency thickness. A nuchal translucency of 3 mm or more identified 25 out of 36 fetuses (69%) with trisomy 21 at the expense of a 4.0% false-positive rate. Correction of nuchal translucency measurements for differences due to variation of the measurement with gestational age, either by using the 'delta-value' or multiples of the median (MoM), did not improve the detection rate in our patient data set. Conclusions. The discriminative capacity of nuchal translucency measurement makes is a useful tool in screening for trisomy 21 and other chromosomal anomalies.