First-trimester Down syndrome screening gets a thumbs up


First-trimester screening using nuchal translucency, PAPP-A (pregnancy-associated plasma protein A), and fß-hCG (the free ß subunit of human chorionic gonadotrophin) is about as effective in detecting Down syndrome as second-trimester screening that uses QUAD testing (alpha fetoprotein, hCG, unconjugated estriol (uE3), and inhibin A) but has fewer false positives, according to results of the FASTER trial presented at the Society for Maternal Fetal Medicine's annual meeting in New Orleans.

With the first-trimester protocol, 76% of cases were detected and only 3.2% of patients received false-positive results. The second-trimester approach detected 84% of cases but had a false-positive rate of 8.4%. When investigators looked at false-positive rates for various detection levels, they found that a fully integrated screening protocol that included nuchal translucency, PAPP-A, and the components of QUAD testing generated the most impressive results: Only 1.4% of women were wrongly told they were at risk for Down syndrome when the detection rate reached 80%. When 90% of cases were caught, the false-positive rate was 5.4%.

Malone FD, Wald NJ, Canick JA et al. First and second trimester evaluation of risk (FASTER) Trial: Principal results of the NICHD multicenter Down Syndrome Screening Study. Am J Obstet Gynecol. 2003;189(6 suppl):S56-S57. (Abstract 1).

Commentary by Charles J. Lockwood, MD, Yale University School of Medicine: It is time to consider such an approach in this country. The research presented at SMFM is very consistent with those of Wald and associates (N Engl J Med. 1999; 341:461-467) who reported that when a risk cutoff of 1/120 was used to define a positive result on an integrated first- and second-trimester screening test, the rate of detection of Down syndrome was 85%, with a false-positive rate of 0.9%. Dr. Wald's data suggest that integration of first- and second-trimester screening results would lead to detection rates comparable or better than can be achieved with either first- and second-trimester screening but with an 80% reduction in the number of invasive diagnostic procedures and consequent losses of normal fetuses.

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