First Trimester is Best Time to Screen Pregnant Women for Fetal Down's Syndrome

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Pregnancy Screening

A new study by researchers for the First and Second Trimester Evaluation of Risk (FASTER) Research Consortium has found that the most optimal and accurate time to screen pregnant women for the presence of fetal Down's syndrome is during the first trimester. The findings of the study will be published as the lead article in the Nov. 10 issue of the New England Journal of Medicine.

Researchers reported that the combination of nuchal translucency, an ultrasound measurement of the area behind the fetal neck, and maternal blood markers measured at 11 weeks gestation results in the detection of 87 percent of cases of Down's syndrome. The study also reports that a combination of first- and second-trimester markers yielded a 96 percent detection rate for Down's syndrome at 11 weeks gestation.

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Down's syndrome is a genetic condition that causes delays in physical and intellectual development and occurs in one out of every 800 births. The chances of fetal Down's syndrome increases with increasing maternal age. Prior to the study's finding, it has been a standard of care for physicians to provide screening and/or diagnostic tests for Down's syndrome during a woman's second trimester of pregnancy.

Currently, the most common screening test for Down's syndrome is the triple or quadruple screen, a series of three or four blood tests. The quadruple screen detects approximately 79 percent of cases of Down's syndrome and is performed between 15 and 21 weeks of gestation. If a patient has a positive quadruple screen, an amniocentesis is offered. Amniocentesis is also commonly offered to women who are age 35 or older at their delivery date.

"When we conducted these studies, we wanted to find the most optimal method to screen pregnant women for the presence of fetal Down's syndrome," said Lorraine Dugoff, M.D., associate professor in the CU School of Medicine's Department of Obstetrics and Gynecology and co-author of the study. "It was our goal to study the effectiveness of first-trimester screening and find the best possible screening test for Down's syndrome."

Dr. Dugoff and her FASTER colleagues performed first- and second-trimester screenings in 38,167 patients nationwide

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