Blood Test may Detect Down Syndrome

MaterniT21 LDT pregnancy maternal test may identify Down Syndrome

(RxWiki News) A highly accurate pre-natal test for Down syndrome is now available. With only a sample of a woman's blood in the first or second trimester of pregnancy, the Down Syndrome genetic developmental disorder can be detected.

Women age 35 and over have a significantly higher risk of having a baby with Down syndrome, caused by an extra chromosome 21. The new test detects cell-free fetal DNA in the maternal blood, to point to the extra chromosome if present.

"Ask your doctor about testing for Down syndrome."

The test is called MaterniT21 LDT, and is currently being offered to physicians in 20 metropolitan areas nationwide. It was evaluated in a clinical validation study of about 4,400 pregnant women who were at high risk for delivering a baby with Down syndrome due to their age, family history or the results of other tests.

The MaterniT21 LDT test was done between 8.1 and 21.5 weeks of pregnancy and results had an accuracy rate of 98.6 percent. Among 212 Down syndrome cases, there were three false negatives. The test had both a sensitivity and specificity percentage of 99.

When applied to high-risk pregnancies, measuring maternal plasma DNA detects nearly all cases of Down syndrome at a very low false-positive rate," wrote lead author Glenn Palomaki, PhD, of Women and Infants Hospital. "This method can substantially reduce the need for invasive diagnostic procedures and attendant procedure-related fetal losses."

Previous testing for Down syndrome has included maternal serum markers and sonograms that together have a sensitivity of about 90 percent and a specificity of 98 percent. Positive results from this kind of testing is usually followed by amniocentesis or chorionic villus sampling, which can injure the fetus or cause miscarriage. 

The maker of the test, Sequenom, plans to seek FDA approval in late 2012 or early 2013, and produce a test kit that other labs can use. It also announced plans to immediately begin working with third-party payers to cover costs of the test, saying that patients would pay no more than $235 out of pocket expenses.

Findings from the study and test were published in the October 2011 issue of Genetics in Medicine.

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Review Date: 
October 24, 2011