What is chorionic villus sampling (CVS)?

Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of 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.

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 13th weeks of pregnancy.

Although exact methods can vary, the procedure involves inserting a needle through the abdominal and uterine wall into the placenta or placing aa small tube called a catheter through a woman's vagina and into her cervix. The procedure follows this process:

• Ultrasound is used to guide the needle or catheter into the placenta. 
• Local anesthesia may be used based if the procedure is performed through the abdomen. 
• Tissue is removed using a syringe on the other end of the catheter. 
• 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. Other times, the doctor obtains a sample that does not have enough cells to test or grow in the laboratory, such that results are incomplete or inconclusive.

What are the risks and benefits of chorionic villus sampling?

The risks of CVS include the following:

• Miscarriage. CVS has a similar or slightly higher rate of pregnancy loss compared to amniocentesis. Consult your doctor for information about loss rates.
• Infection. CVS is an invasive procedure and may cause infection.
• Limb defects. Some reports show that babies born after CVS may have an increased rate of limb (arm, leg, or finger) defects when CVS is performed before 10 weeks of pregnancy.

The benefits of CVS include the following:

• Early diagnosis of a chromosomal abnormality
• Early diagnosis of certain genetic defects

Be sure to discuss the risks and benefits of CVS more specifically with your doctor.