K_Z
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Thanks, Jenny. Of course the test isn't 100% accurate. An amniocentesis is necessary to be sure, IIRC. My daughter tested positive for Down's Syndrom with all three of her children. She and her husband decided they would not abort any of the children even if they were born with DS, so there was no point in testing further.
We--their parents--all promised to support whatever decision they made, of course, and promised to help if they had a a child with special needs. Thankfully, all three children were born normal, and above-normal in intelligence.
BBM.There are 2 kinds of prenatal tests: screening tests, and diagnostic tests. Diagnostic tests are virtually 100% accurate. Screening tests have varying rates of accuracy depending on variables.
Chorionic villi sampling is a diagnostic test. It is virtually 100% accurate for diagnosing Down Syndrome.
(This isn't a scholarly reference, but it's accurate.)
What kind of problems does CVS detect?
Like amniocentesis, CVS can identify:
•Nearly all chromosomal abnormalities, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). The test is more than 99 percent accurate in identifying these conditions, though it can't measure their severity.
•Several hundred genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. The test is not used to look for all of them, but if your baby is at increased risk for one or more of these disorders, CVS can usually tell you whether he has the disease.
Unlike amniocentesis, CVS cannot detect neural tube defects, such as spina bifida. If you opt for CVS, you'll be offered a blood screening test in your second trimester to determine whether you're at increased risk for neural tube defects. Most neural tube defects can be detected by a detailed second-trimester ultrasound done at a state-of-the-art academic center.
http://www.babycenter.com/0_chorionic-villus-sampling-cvs_328.bc