Definition Chorionic villus sampling, or CVS, is a procedure in which a small piece of tissue is taken from the chorionic villi early in pregnancy. The chorionic villi are lacy fibrils that attach the sac holding the foetus to the uterine wall. These fibrils have the same genetic and biochemical makeup as the foetus.
Who is a candidate for the procedure? A woman may wish to have CVS done if one of the following conditions applies:
she will be 35 years old or older when her baby is born
she or her partner has had a child or foetus with a chromosomal abnormality
she or the father has a family history of a serious chromosomal abnormality
the baby might have a serious problem passed on only to one sex, such as muscular dystrophy
she wants to find out if her baby has a serious health problem that can be detected by examining its genes
Chorionic villi sampling can detect many disorders in a foetus, including the following:
cystic fibrosis, a condition in which abnormal body secretions cause problems in the lungs and digestive system
Down syndrome, which causes mental retardation and health problems
phenylketonuria, or PKU, which interferes with the body's ability to handle certain food components
sickle cell anaemia, a condition in which abnormal red blood cells interfere with many body processes
Tay-Sachs disease, which causes blindness, loss of function, and early death
CVS is usually performed 10 to 12 weeks after the woman has missed a period. An amniocentesis is a similar procedure that involves taking a sample of the fluid in the sac surrounding the foetus. It is done several weeks later. If there is a possibility that the couple wants to terminate the pregnancy, CVS gives results earlier. The abortion can then be done earlier, when it is safer for the woman. For many people, this is a key reason to have CVS.
However, a CVS does not detect spina bifida or other neural tube defects. A blood test known as alpha-fetoprotein can be done to screen for these disorders.
How is the procedure performed? Shortly before the procedure, the woman will be asked to fill her bladder. The full bladder helps the doctor see the pelvic organs with an ultrasound. The doctor uses the ultrasound to guide the insertion of a thin needle. Depending on the position of the placenta and the uterus, CVS may be done through the vagina or through the abdominal wall.
If the route is through the vagina, that area is cleaned with an antiseptic. A tube is put through the cervix, or opening to the uterus. A sample of the fibrils is suctioned out. If CVS is done through the abdomen, a local anaesthetic helps to numb the skin. Then, a needle is put through the wall of uterus and a sample of the fibrils is drawn up into the needle. The tissue sample is sent to a laboratory for testing.
What happens right after the procedure? The woman is allowed to go home shortly after the procedure.
What happens later at home? After a CVS, the woman should avoid strenuous exercise for 1 to 2 days. One out of five women have cramps after a CVS. One out of three have vaginal bleeding or spotting. These effects usually stop within a few days. Preliminary results from the test will be available in 3 to 4 days. Final results are usually ready within 2 weeks.
What are the potential complications after the procedure? The biggest risk of CVS is miscarriage. It occurs in 1 to 2 out of 100 cases. This is slightly higher than the risk with amniocentesis, which causes miscarriage in 1 out of 200 cases. There is also a slight risk of infection from the procedure. Any new or worsening symptoms should be reported to the doctor.
Author: Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 06/06/2001 Contributors Potential conflict of interest information for reviewers available on request
