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Missing fetal nasal bone refines trisomy 21 Dx. (Ultrasound Screening at 11-14 Weeks).

Ultrasound screening for the absence of a fetal nasal bone at 11-14 weeks' gestation is a new technique that offers promise for further refining the prenatal diagnosis of trisomy 21, according to Dr. Simona Cicero of King's College Hospital Medical School, London, and her associates.

The researchers performed ultrasound evaluation on 701 fetuses who were considered to be at risk for the chromosomal abnormality because of advanced maternal age and a previous finding of nuchal translucency

Among 59 fetuses later determined by chorionic villus sampling and fetal karyotyping to have trisomy 21, the nasal bone was noted to be absent on ultrasound in 43 (73%). In comparison, among the 603 normal-karyotype fetuses, the nasal bone was absent in only 3 (0.5%).

Screening for trisomy 21 by maternal age and ultrasound detection of nuchal translucency has been estimated to have a sensitivity of 75% and a false-positive rate of 5%. The sensitivity could rise to 85% and the false-positive rate could decrease to about 1% if ultrasound screening also detected the absence of the fetal nasal bone.

Furthermore, "a sensitivity of more than 90% could probably be achieved by the comb nation of nasal bone, nuchal translucency thickness, and firs-trimester maternal serum biochemistry," hey wrote (Lancet 358[9294]:1665-67, 2001).

An editorial accompanying he article points out the "compelling" advantages of first-trimester, noninvasive screening using these techniques, including the possibility for "less traumatic" abortion for some but "earlier r assurance" for most (Lancet 35/[9294]1658-59,2001).
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Author:Walsh, Nancy
Publication:OB GYN News
Date:Feb 1, 2002
Words:247
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