INTRODUCTION — Chorionic villus sampling (CVS) is a procedure that may be performed during pregnancy to diagnose certain genetic or chromosomal disorders. CVS involves having a biopsy of the developing placenta. The chorionic villi are the tiny units that make up the placenta and have the same genetic make-up as the fetus.

More detailed information about CVS is available by subscription. (See "Chorionic villus sampling".)

WHY IS CHORIONIC VILLUS SAMPLING DONE? — CVS is a procedure to obtain cells of fetal origin. Tests on these cells in the laboratory can diagnose a variety of fetal genetic conditions, including chromosome anomalies (such as Down syndrome), inherited genetic disorders (such as Tay-Sachs disease and cystic fibrosis), or very tiny duplications or deletions of sections of fetal DNA, in which all genetic information is coded. The choice of the most appropriate laboratory tests to perform generally depends on the reason for the test, which your health care provider will discuss with you. CVS is generally performed during the first trimester of pregnancy, at 10 to 12 weeks, and the results are available within a couple of weeks.

Amniocentesis can provide similar information, but it can only be done later in pregnancy (typically at 15 to 17 weeks). (See "Patient education: Amniocentesis (Beyond the Basics)".)

Your health care provider may recommend CVS if:

●You have a family history of a genetic disorder.

●You and your husband are carriers for genetic disorders, such as fragile X, Tay-Sachs disease, or cystic fibrosis.

●Prenatal screening tests (blood tests or ultrasound) show that your fetus is at increased risk of having a genetic disorder. For example, ultrasound may detect a fetal abnormality.

CVS or amniocentesis? — CVS provides results in the first trimester. However, the procedure has a slightly higher risk of miscarriage compared with amniocentesis.

You may want to know if your fetus has a genetic disorder early in your pregnancy for several reasons:

●Your pregnancy may still be relatively private, not known by family, friends, and acquaintances.

●If you would consider terminating your pregnancy based on the results of testing, pregnancy termination is somewhat safer early in pregnancy. (See "Patient education: Abortion (pregnancy termination) (Beyond the Basics)".)

WHAT DOES A POSITIVE OR NEGATIVE TEST MEAN? — A positive result suggests that the baby has the genetic problem tested for. Sometimes more tests are needed to confirm this. It may be necessary to perform genetic testing on a blood sample from the parents or additional tests on the baby may be needed, and this may require amniocentesis.

A negative result generally means that the baby does not have the specific genetic disease tested for, but there are some exceptions. For example, the sample of placental cells that was tested may not have been positive for the genetic disease, but the fetus itself may still have positive cells and thus may exhibit characteristics of the disease.

Also, a negative result only means that the test was negative for the specific abnormalities tested for, such as Down syndrome. The baby could still have physical birth defects or genetic disorders that were not tested for. It is not possible to test for all genetic disorders when CVS is performed.

CHORIONIC VILLUS SAMPLING PROCEDURE — There are two ways to perform CVS: through the cervix (called transcervical) and through the abdomen (transabdominal). The choice is based largely on where the placenta is attached to the uterus. With both methods, the procedure is performed while having an ultrasound.

Transcervical CVS — In the transcervical CVS technique, the physician inserts a small tube through the opening in the cervix into the placenta. This is done while ultrasound guides the physician (figure 1).

Transabdominal CVS — In the transabdominal CVS technique, the physician inserts a needle through the abdomen into the placenta. This is also done with ultrasound to guide the physician (figure 2).

The physician can usually obtain enough placental tissue the first time he or she inserts the needle or tube into the placenta. However, if there is not enough tissue, the physician may need to try again.

CHORIONIC VILLUS SAMPLING COMPLICATIONS — The most serious complication of CVS is miscarriage. CVS does not increase the risk of the fetus dying later in the pregnancy or after birth.

Miscarriage — Miscarriage can happen in any pregnancy. However, the risk of miscarriage is higher in women who have CVS compared with those who choose amniocentesis for prenatal diagnosis. The excess risk of miscarriage in pregnancies undergoing CVS is confined to transcervical CVS, which carries a significantly greater risk of fetal loss than amniocentesis. Transabdominal CVS appears to carry a fetal loss rate related to the procedure similar to that of amniocentesis, with a procedure-related pregnancy loss rate of 0.7 percent within 14 days and of 1.3 percent within 30 days [1].

Bleeding — It is normal to have some vaginal spotting after CVS. If you have heavier bleeding (eg, like a menstrual period), call your health care provider.

CVS can cause small amounts of fetal blood to be released into your bloodstream. This can potentially cause complications in future pregnancies, especially if you have an Rh negative blood type (eg, O negative). If you have an Rh negative blood type, you will be given Rh(D) immune globulin after the procedure to prevent this complication.

Repeat testing — Some women who have a CVS will need a repeat CVS or amniocentesis. This can happen if the results of your first test are unclear, if the cells do not grow in the laboratory, or if there was not enough tissue collected.

WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for health care professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Chorionic villus sampling (The Basics)
Patient education: Should I have testing for Down syndrome during pregnancy? (The Basics)
Patient education: Amniocentesis (The Basics)
Patient education: Prenatal care (The Basics)
Patient education: Pregnancy in Rh-negative people (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Amniocentesis (Beyond the Basics)
Patient education: Abortion (pregnancy termination) (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Chorionic villus sampling
First-trimester combined test and integrated tests for screening for Down syndrome and trisomy 18
Fetal blood sampling

The following organizations also provide reliable health information.

●National Library of Medicine

(https://medlineplus.gov/healthtopics.html)

●March of Dimes

(https://www.marchofdimes.org/)

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