Chorionic Villus Sampling
Chorionic villus sampling, abbreviated as 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 unborn child to the uterine wall. These fibrils have the same genetic and biochemical makeup as the child.
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 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 an unborn child, 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 (PKU), which interferes with the body's ability to handle certain food components
sickle cell anemia, a condition in which abnormal red blood cells interfere with many body processes
Tay-Sachs disease, an inherited condition 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 unborn child. It is done several weeks later. If there is a possibility that the couple wants to terminate the pregnancy, CVS gives results earlier than amniocentesis, allowing the abortion can then be done earlier, when there are fewer risks of medical complication.
For many people, this is a key reason to have CVS. However, a CVS does not detect spina bifida, or other neural tube defects, and has a slightly higher risk of non-diagnosis due to placental tissue contamination. 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 healthcare professional see the pelvic organs with an ultrasound. The professional 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 anesthetic 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 lab for testing.