Chorionic Villi Sampling
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal test used to identify various genetic problems, including Down syndrome. Using a thin tube guided through your cervix or a needle inserted into your uterus, your health care provider takes a sample of chorionic villi from the placenta. These wispy projections from the placenta — which have the same genetic makeup as your baby — transfer nutrients, oxygen and antibodies from you to your baby.
Who might need chorionic villus sampling?
Chorionic villus sampling can provide genetic information about your baby earlier in your pregnancy than can other diagnostic tests, such as amniocentesis. The test might be offered if your baby has an increased risk of a specific chromosomal or genetic disorder. In other cases, chorionic villus sampling may be recommended if the results of a screening test in the first trimester cause concern. Chorionic villus sampling cannot detect neural tube defects, such as spina bifida. If neural tube defects are a concern, an ultrasound or genetic amniocentesis may be recommended instead.
When is chorionic villus sampling done?
Chorionic villus sampling is usually done between the ninth and 14th weeks of pregnancy. Amniocentesis is typically done after the 15th week of pregnancy.
What can chorionic villus sampling reveal?
Analysis of fetal cells can reveal whether your baby has a chromosomal abnormality, such as Down syndrome. Chorionic villus sampling can also be used to test for other genetic disorders, such as Tay-Sachs disease — but only if there is a specific reason to test for these conditions.
What are the risks?
Chorionic villus sampling carries various risks, including:
- Miscarriage. Chorionic villus sampling has a one in 100 risk of miscarriage.
- Cramping and vaginal bleeding. You may feel cramping after the test. Vaginal bleeding also is possible, especially if the cell sample was taken through your cervix. If you develop heavy bleeding or a fever after chorionic villus sampling, contact your health care provider.
- Rh sensitization. Chorionic villus sampling may cause some of the baby's blood cells to enter your bloodstream. If you have Rh-negative blood and your baby has Rh-positive blood, you'll be given a drug called Rh immunoglobulin after the test to prevent you from producing antibodies against your baby's blood cells.
Chorionic villus sampling is recommended when the potential value of early diagnostic results outweighs the risk of miscarriage or other complications. Ultimately, the decision to have chorionic villus sampling is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.
What happens after chorionic villus sampling?
Most test results are normal, which can ease anxiety about your baby's health. Sometimes a follow-up ultrasound is recommended several days after chorionic villus sampling to verify the baby's well-being. Rarely, CVS results are unclear and amniocentesis is needed to clarify the diagnosis.
Early diagnosis of certain disorders may lead to early treatment. For example, if a female baby has congenital adrenal hyperplasia — a condition in which excessive amounts of male hormones are produced — hormone therapy can be given to the mother to prevent the baby from developing male characteristics.
If chorionic villus sampling indicates that your baby has a chromosomal problem or a genetic disorder that can't be treated, you may be faced with wrenching decisions — such as whether to continue the pregnancy. Seek support from your health care team, your loved ones and other close contacts during this difficult time.
Credit: National Institute of Health.