A study of more than 38,000 pregnant women at 15 U.S. centers demonstrated the high accuracy of non-invasive screening for Down syndrome ( also known as trisomy 21 ) in the first trimester of pregnancy, at 11 weeks.

The findings are a significant advantage over the current standard screening, a blood test performed in the second trimester of pregnancy.

" These results will undoubtedly change the practice – all pregnant women should have the option of early screening for Down syndrome in their first trimester," said Mary E. D'Alton, principal investigator of the study. She is Chair of the Department of Obstetrics and Gynecology at Columbia University College of Physicians and Surgeons, and Chief of Obstetrics and Gynecology at NewYork-Presbyterian Hospital/Columbia. " Down syndrome screenings based on either maternal age alone, or an ultrasound or sonogram alone, are no longer justified protocols."

Published in the New England Journal of Medicine ( NEJM ), the study is known as the FASTER trial ( First and Second Trimester Evaluation of Risk ).

The new screening approach uses a blood test that analyzes the level of a protein and hormone in the mother's blood, combined with an ultrasound or sonogram picture of the thickness of skin on the back of the baby's neck ( known as the nuchal translucency or NT ).

Results are available within five days, often before starting the second trimester of pregnancy.

This combination approach determines the odds that the baby might have Down syndrome, allowing pregnant women the option of prenatal diagnosis for Down syndrome and other chromosomal abnormalities within the first trimester or pregnancy.

The researchers found higher detection – 87 percent – in the first trimester compared to the best second trimester screening method – 81 percent detection. Results with this new combination screening approach in the first trimester are a significant advantage over the current standard screening test.

First-trimester screening was performed on 38,167 patients; 117 were found to have a fetus with Down syndrome. If a positive result was found via screening, the woman was given the option to have the finding confirmed with a diagnostic exam: chorionic villus sampling ( CVS ) or amniocentesis. Both tests carry risks of complication leading to miscarriage.

Down syndrome is one of the leading causes of mental retardation and birth defects, found in one in 660 pregnancies. Persons with this condition have distinct physical features and commonly have certain birth defects and medical problems. Any woman can have a baby with Down syndrome, regardless of her age, race, health, economic status or family history. For this reason, most pregnant women undergo testing to determine their potential to have a baby with this syndrome.

Source: Columbia University Medical Center, 2005


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