Chorionic villus sampling can provide information about your baby's genetic makeup. Generally, chorionic villus sampling is offered when the test results might have a significant impact on the management of the pregnancy — or your desire to continue the pregnancy. Typically, the value of this information can be assessed only by you and your partner.

Chorionic villus sampling is usually done between weeks 10 and 12 of pregnancy — earlier than other prenatal diagnostic tests, such as amniocentesis.

You might consider chorionic villus sampling if:

  • You had positive results from a prenatal screening test. If the results of a screening test — such as the first trimester screen or noninvasive prenatal testing — are positive or worrisome, you might opt for chorionic villus sampling to confirm or rule out a diagnosis.
  • You had a chromosomal condition in a previous pregnancy. If a previous pregnancy was affected by Down syndrome or another chromosomal condition, this pregnancy is at higher risk, too.
  • You're 35 or older. Babies born to women 35 and older have a higher risk of chromosomal conditions, such as Down syndrome.
  • You have a family history of a specific genetic condition, or you or your partner is a known carrier of a genetic condition. In addition to identifying Down syndrome, chorionic villus sampling can be used to diagnose many other genetic conditions — such as Tay-Sachs and cystic fibrosis.

Chorionic villus sampling can't detect neural tube defects, such as spina bifida. If neural tube defects are a concern, an ultrasound or genetic amniocentesis might be recommended instead.

Your health care provider might caution against transcervical chorionic villus sampling — which is done through the vagina — if you have:

  • Vaginal bleeding or spotting in the previous two weeks
  • A cervical infection
  • Cervical narrowing or blockage (cervical stenosis)
  • Involuntary spasms of the muscles of the vaginal wall (vaginismus)
  • An inaccessible placenta, due to a tilted uterus or noncancerous growths in the lower part of your uterus (uterine fibroids)

Rarely, your health care provider might caution against transabdominal chorionic villus sampling — which is done through the abdominal wall — if:

  • Your uterus is severely titled backward and you have intestinal loops between your abdominal wall and uterus
  • Your placenta is located at the back of your uterus and your baby is blocking access to it

Rhesus (Rh) factor — an inherited trait that refers to a specific protein found on the surface of red blood cells — matters, too.

Your health care provider might caution against both types of chorionic villus sampling if you're Rh negative, your baby's father is Rh positive and you're sensitized — your body has already begun to produce antibodies after exposure to the baby's red blood cells at some point during pregnancy. If you're sensitized and have chorionic villus sampling, you're at increased risk of complications following chorionic villus sampling.

Oct. 10, 2012