Measurement of nuchal translucency and the prenatal diagnosis of Down syndrome.

OBJECTIVES: To estimate the sensitivity of nuchal-translucency measurement and compare it with that of second-trimester serum screening using population-based data and to evaluate the effect of nuchal-translucency measurement on the gestational age at prenatal diagnosis of Down syndrome and pregnancy termination.
METHODS: We used The Paris Registry of Congenital Malformation data on 594 cases of Down syndrome (live births, fetal deaths, and pregnancy terminations) from 2001-2006. Analyses were done separately for women younger than 38 years and women aged 38 years or older. Analyses included binomial regression and fractional polynomials to model time trends in gestational age at diagnosis and at pregnancy termination.
RESULTS: Ninety percent of the fetuses had undergone nuchal-translucency measurement as compared with only 22% that underwent second-trimester serum screening. This was principally because half of the pregnant women were given a diagnosis of Down syndrome during the first trimester after an abnormal result of nuchal-translucency measurement. Second-trimester serum screening had a higher sensitivity than did nuchal-translucency measurement (72% compared with 56%). The increasing use of nuchal-translucency measurement led to an increase in early diagnosis of Down syndrome in women younger than 38 years of age; diagnosis before 15 weeks of gestation increased from 21.7% in 2001 to 51.6% in 2006 (P=.016). Pregnancy termination before 15 weeks also increased from 18.8% in 2001 to 47.5% in 2006 (P=.02).
CONCLUSION: The main effect of the increased use of nuchal-translucency measurement was a substantial increase in the early detection of Down syndrome, principally in younger women. This is an important advantage because several studies have shown that women prefer early diagnosis of Down syndrome. LEVEL OF EVIDENCE: III.