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.

Chorionic villus sampling is usually done between weeks 10 and 13 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 prenatal cell-free DNA screening — 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 — including single gene disorders such as Tay-Sachs and cystic fibrosis.

Chorionic villus sampling can't detect certain birth defects, such as neural tube defects. 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:

  • An active cervical or vaginal infection, such as herpes
  • Vaginal bleeding or spotting in the previous two weeks
  • 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 titled backward and your placenta is located at the back of your uterus

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 is Rh positive and your body has already begun to produce Rh antibodies. Bleeding caused by the procedure could increase your antibody response and cause pregnancy complications.

Oct. 17, 2015