What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal test that diagnoses chromosomal abnormalities such as Down syndrome, as well as a host of other genetic disorders. The doctor takes cells from tiny fingerlike projections on your placenta called the chorionic villi and sends them to a lab for genetic analysis.
Women who choose to have CVS or amniocentesis are often those at increased risk for genetic and chromosomal problems, in part because these tests are invasive and carry a small risk of miscarriage.
The main advantage of CVS over amniocentesis is that you can have it done earlier — generally between 10 and 13 weeks of pregnancy. For an amnio, you’ll have to wait until you’re at least 16 weeks pregnant.
What kind of problems does CVS diagnose?
Like amniocentesis, CVS can identify:
- Nearly all chromosomal abnormalities, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome). The test can diagnose these conditions, but 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.
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