Prenatal Down syndrome detection: expert recommends integrated over sequential screening.(Obstetrics)

KISSIMMEE. FLA. -- With first-trimester testing becoming more widely accepted to assess risk for Down syndrome, physicians should not screen in both first and second trimesters unless the findings are integrated and presented during the second trimester as a unified result, speakers said at a meeting sponsored by the American College of Medical Genetics.

"A screening test should not be followed by another screening test; it should be followed by a diagnostic test," Dr. Alan E. Donnenfeld said. "We're going to tell [the patient] the risk is increased or decreased and let her decide if she wants to pursue prenatal diagnosis. Diagnostic tests give you answers."

Chorionic villus sampling and amniocentesis can tell with almost 100% certainty whether the fetus has a chromosomal abnormality. Screening cannot, said Dr. Donnenfeld of the department of obstetrics and gynecology at Drexel University, Philadelphia.

Sequential screening increases both the false-positive rate, with its associated anxiety and concern, and the amniocentesis rate, with the risk of iatrogenic pregnancy loss. It produces only marginal improvement in the detection rate and can result in conflicting risk estimates, causing confusion for the physician and patient.

"Sequential screening is undesirable in a public health program and can cause needless distress to individuals," said Dr. Nicholas J. Wald, professor and head of the Centre for Environmental and Preventive Medicine at Wolfson Institute of Preventive Medicine, London, and lead researcher on the Serum, Urine, and Ultrasound Screening Study (SURUSS), which investigated integrated prenatal screening for Down syndrome.

Although screening does not detect all Down syndrome pregnancies, using an integrated screen is one way to increase the detection rate. Screenings are done during the first and second trimesters but presented as a single combined risk result. First- and second-trimester screenings offer similar detection rates; when they are used ...