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.
Chorionic villus sampling (CVS) is an alternative to amniocentesis. The advantage of CVS is that it can be done earlier, between the tenth and twelth weeks of pregnancy. Late CVS or placental biopsy, when indicated, also can be performed after 12 weeks gestation. This test is used to diagnose chromosomal abnormalities and other genetic diseases in your baby.
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.
Women with twins or other multiples usually need sampling from each placenta. However, because of the complexity of the procedure, and positioning of the placentas, CVS is not always feasible or successful with multiples.
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. In some cases there is an active vaginal infection such as herpes or gonorrhea, which will prohibit the procedure. Other times the physician obtains a sample that does not have enough tissue to grow in the laboratory, such that results are incomplete or inconclusive.
The main advantage of CVS is that it is performed at an earlier time in the pregnancy than an amniocentesis. With CVS, results are generally available by 14 weeks of pregnancy. This gives the patient early reassurance if the results are normal, or more time to consider her options if problems are detected.