Chorionic Villus Sampling
What is a 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 10th and 12th 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.
How is CVS 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. Although exact methods can vary, the procedure involves inserting a small tube called a catheter through a woman's vagina and into her cervix and usually follows this process:
- Ultrasound is used to guide the catheter into place near the placenta.
- Tissue is removed using a syringe on the other end of the catheter.
- Another method is transabdominal CVS, which involves inserting a needle through the woman's abdomen and into her uterus to sample the placental cells.
- Women may feel some cramping during and after the CVS procedure.
- The tissue samples are sent to a genetic laboratory to grow and be analyzed. Results are usually available in about 10 days to two weeks, depending on the laboratory.
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.
You may consider having CVS because:
- You have screening results showing an increased risk for a chromosomal abnormality.
- Your pregnancy is at risk for an inherited genetic condition such as Tay-Sachs disease, sickle cell anemia, cystic fibrosis, fragile X or other conditions for which testing is available.
- You have a family or personal history of a chromosomal abnormality or a genetic condition.
Before the CVS procedure, you will meet with a genetic counselor to review your family history, discuss the testing, and set up an appointment for the testing.
Benefits of Chorionic Villus Sampling
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 you early reassurance if the results are normal, or more time to consider your options if problems are detected.
Normal results on CVS can provide reassurance that the fetus does not have a chromosome abnormality or the genetic condition for which it is tested. However, it does not rule out all problems. Any pregnancy carries about a 3 to 5 percent risk for birth defects and/or developmental disabilities regardless of mother's age, use of medications or a family history.
To learn more, contact a Women’s Health maternal fetal medicine specialist or request an appointment today.