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Early screening for down syndrome: noninvasive.

NEW ORLEANS -- First-trimester Down syndrome screening was at least as effective as second-trimester screening in a major U.S. trial expected to pave the way for a shift in the standard of care for pregnant women who desire an early, noninvasive method to assess fetal risk of the disorder.

The First and Second Trimester Evaluation of Risk (FASTER) trial involved about 38,000 pregnant women at 15 centers who underwent combined first-trimester screening with nuchal translucency measurement and serum testing for the biochemical markers pregnancy-associated plasma protein A (PAPP-A) and free [beta]-HCG. The women also underwent second-trimester quad screening; second-trimester screening is the current standard of care.

A total of 84 babies were born with Down syndrome in this study. The detection rate for combined first-trimester screening was 83% with a false-positive rate of 5.6%, and the detection rate for second-trimester screening was 85% with a false-positive rate of 8.5%; these differences were not statistically significant. The best results were achieved using both first- and second-trimester testing, which yielded a 94% detection rate and 11% false positive rate, Dr. Fergal D. Malone reported at the annual meeting of the Society for Maternal-Fetal Medicine.

First-trimester screening was conducted between 10 3/7 weeks" and 13 6/7 weeks" gestation, although the optimal time for testing was 11 weeks, because nuchal translucency was shown to deteriorate rapidly as a marker between 11 and 13 weeks. Second-trimester screening was conducted between 15 and 18 weeks' gestation.

Participants with any positive screen were offered genetic counseling and amniocentesis, said Dr. Malone of Columbia University, New York.

"The FASTER trial shows that both first-trimester combined screening and second-trimester quad screening are similarly effective for Down syndrome. Additionally, integrated screening across both the first and second trimester is the most efficient test in cases when [chorionic villi sampling] is either not desired or not readily available," he said, noting that these and other findings from the trial suggest that screening based on nuchal translucency or maternal age, or second-trimester triple screening alone, is no longer justifiable.

The findings have significant implications for pregnant women, particularly those initially perceived to be at high risk because of advanced age, said Dr. Mary E. D'Alton, principal investigator for the FASTER trial. Negative screening in the first trimester would allow these women to avoid invasive fetal testing.

The findings also demonstrate a clearcut advantage with first-trimester screening for any woman who wants the earliest Down syndrome diagnosis possible. They also identify the safest approach for screening--that is, integrated first- and second-trimester screening, which will reduce the need for amniocentesis, compared with either type of screening alone--in those who want a more definitive diagnosis, said Dr. D'Alton, also of Columbia University.

Currently, about half of all perinatologists are using combined first-trimester screening, but rapid nationwide implementation of this approach could be problematic because nuchal translucency is a difficult method of screening to perform well consistently. Standardization of the screening method is needed, as are educational programs and ongoing quality assessment, Dr. D'Alton and Dr. Malone agreed.

"Extensive implementation needs have to be solved," Dr. Malone said. "I don't think we're ready yet to say every general practitioner out there should be doing nuchal translucency screening ... but I know the [Society of Maternal-Fetal Medicine] and other professional bodies are trying to put some leadership into place to give some guidance on who should do nuchal translucency--whether it should be generalists or just perinatologists."

A multiorganization workshop to address the FASTER findings is planned for July 22-23. It is being organized by the National Institutes of Health, the American College of Obstetricians and Gynecologists, and the Society for Maternal-Fetal Medicine.


Tallahassee Bureau
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Title Annotation:First and Second Trimester Evaluation of Risk trial
Author:Worcester, Sharon
Publication:Family Practice News
Geographic Code:1USA
Date:Mar 1, 2004
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