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

Objective: To examine the discriminate 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 it a useful tool in screening for trisomy 21 and other chromosomal anomalies.