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First-Trimester Screening Can Detect Down Syndrome

Combined screening at 11 weeks gets better results than similar screening at 13 weeks

WEDNESDAY, Nov. 9 (HealthDay News) -- Screening for Down syndrome at 11 weeks using three different methods produces better results than quadruple screening performed in the second trimester, according to a study in the Nov. 10 issue of the New England Journal of Medicine. However, combining the results from the first and second trimesters yields a high detection rate (more than 95%) with a low false-positive rate, the authors note.

Fergal D. Malone, M.D., of the Columbia University College of Physicians and Surgeons in New York, and colleagues conducted a study of 38,167 women to compare the accuracy of first- and second-trimester screening for Down syndrome.

First-trimester combined screening included nuchal translucency measurement, pregnancy-associated plasma protein A and the free beta subunit of human chorionic gonadotropin. Second-trimester quadruple screening included measurement of alpha-fetoprotein, total human chorionic gonadotropin, unconjugated estriol and inhibin A at 15 through 18 weeks of gestation.

Combined screening at 11 weeks produced better results than second-trimester quadruple screening: 87% versus 81% detection rate with a 5% false-positive rate. However, detection rates declined if combined screening was delayed until 13 weeks. Overall, stepwise sequential and fully integrated screening with first testing at 11 weeks had high detection rates (95% and 96%, respectively) and low false-positive rates (5%).

"When there is appropriate quality control for measurement of nuchal translucency, first-trimester combined screening is a powerful tool for the detection of Down syndrome," the authors conclude.

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