Chorionic Villus Sampling
What is chorionic villus sampling (CVS)?Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of some of the placental tissue. This tissue contains the same genetic material as the fetus and can be tested for chromosomal abnormalities and some other genetic problems. Testing is available for other genetic defects and disorders depending on the family history and availability of laboratory testing at the time of the procedure. In comparison to amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test between 16 to 18 weeks of their pregnancy, to screen for neural tube defects.
How is chorionic villus sampling performed?CVS may be offered to women who are at increased risk for chromosomal abnormalities or have a family history of a genetic defect that is testable from the placental tissue. CVS is usually performed between the 10th and 12th weeks of pregnancy, either:
- Ultrasound is used to guide the catheter or needle into the placenta.
- Tissue is removed using a syringe on the other end of the catheter or needle.
- Women may feel some cramping during and after the CVS procedure.
- Light bleeding may occur normally after transcervical CVS.
- The tissue samples are sent to a genetic laboratory to grow and be analyzed. Results are usually available in about two weeks.
Some women may not be candidates for CVS or may not obtain results that are 100 percent accurate, and may, therefore, require a follow-up amniocentesis. The presence of vaginal infections such as herpes or gonorrhea may prohibit the procedure. Rarely, some samples are too small or do not grow in the laboratory, and follow-up amniocentesis is recommended.
What are the risks and benefits of chorionic villus sampling?The risks of CVS include the following:
In experienced Centers with skilled practitioners, the pregnancy loss rate for CVS is comparable to amniocentesis.
Like amniocentesis, CVS is an invasive procedure and carries a small risk for infection.
- limb defects
In experienced hands, CVS does not carry an increased risk for limb defects, except when CVS is performed before 10 weeks of pregnancy.
- early diagnosis of a chromosomal abnormality
- early diagnosis of certain genetic defects
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