Most Down Syndrome Markers Deemed Unreliable.

None of the markers for Down syndrome on second-trimester ultrasonography are sensitive enough to reliably discriminate between affected and unaffected fetuses, a metaanalysis of 56 studies involving over 132,000 pregnancies has shown.

Physicians routinely counsel patients that the presence of one of these markers indicates an increased risk for Down syndrome and warrants amniocentesis for a definitive diagnosis. Not only do the data refute such risk estimates, they also suggest that this common clinical practice often does more harm than good, according to Dr. Rebecca Smith-Bindman of the University of California, San Francisco, and her associates.

"Clinicians should be very cautious about the use of these markers to counsel women about their risk of having a fetus with Down syndrome," they said (JAMA 285[8]:1044-55, 2001).

Their metaanalysis included studies that measured the true-positive, false-positive, true-negative, and false-negative results for each of eight isolated ultra sound markers for Down syndrome: nuchal-fold thickening, choroid plexus cyst, echogenic intracardiac focus, echogenic bowel, renal pyelectasis, shortened humerus, shortened femur, and fetal structural malformations.

Only one of these markers, a thickened nuchal fold, helped distinguish affected from unaffected fetuses. But a thickened nuchal fold is present in so few fetuses with Down syndrome that ultrasound screening for it remains impractical, the investigators said.

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