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 chromosomes as the fetus.

More detailed information about chorionic villus sampling is available by subscription. (See "Chorionic villus sampling: Risks, complications, and techniques".)

WHY IS CVS DONE?

CVS can test for conditions such as Down syndrome, Tay Sachs disease, and cystic fibrosis. It is generally performed during the first trimester of pregnancy, at 10 to 12 weeks, and the results are available within a few days.

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

Your healthcare provider may recommend CVS if:

• You have a family history of a genetic disorder, such as Down syndrome, Tay Sachs disease, or cystic fibrosis. Having a family history increases the chances of inheriting the condition.
• Prenatal testing (blood tests or ultrasound) shows that your fetus is at increased risk of having a genetic disorder.

CVS or amniocentesis? — CVS provides results as soon as possible in the first trimester. However, the procedure has a slightly higher risk of miscarriage compared to 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 information: Abortion (pregnancy termination)".)

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 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 to those who do not. For every 100 women who undergo CVS, approximately one woman will have a miscarriage as a result of the procedure. Amniocentesis can also cause miscarriage, although the risk is lower than with CVS.

Bleeding — It is normal to have some vaginal spotting after CVS. If you have heavier bleeding (eg, like a menstrual period), call your healthcare 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 Rhogam (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 healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed every four months on our web site (www.uptodate.com/patients).

Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information

Patient information: Amniocentesis
Patient information: Abortion (pregnancy termination)

Professional level information

Basic principles of genetic counseling for the obstetrical provider
Chorionic villus sampling: Risks, complications, and techniques
Fetal blood sampling: Indications and invasive fetal therapy
First trimester and integrated screening for Down syndrome and trisomy 18

The following organizations also provide reliable health information.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/healthtopics.html)

• March of Dimes

      (www.marchofdimes.com)

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