Chorionic villus sampling (CVS)

Chorionic villus sampling or CVS is a diagnostic procedure performed in the late first trimester or early second trimester that involves obtaining a small tissue sample of chorionic villi from the placenta.  

What are the indications for CVS testing? 

CVS testing is most commonly performed for evaluation of fetal karyotype (chromosomes) due to increased risk of fetal chromosomal abnormalities associated with advanced maternal age (AMA).  Other indications include having a previous pregnancy or child with a chromosomal abnormality, family history of chromosomal abnormality, parental chromosomal abnormality, abnormal first trimester screening for Down syndrome, or family history of other genetic disease / syndrome or inherited metabolic abnormality for which prenatal diagnostic testing is available. 

When is CVS performed?

CVS procedures are generally performed between 10 and 13 weeks of gestation.  In some circumstances it may be performed as early as 9 weeks or as late as 14 weeks of gestation.  In pregnancies complicated by decreased amniotic fluid volume, CVS may be performed at even later gestational ages.

How is the CVS procedure performed? 

Genetic counseling is provided prior to finalizing a decision regarding early pregnancy testing by CVS.  A detailed ultrasound is performed for evaluation of fetal and maternal anatomy, and careful evaluation of the placental implantation sight. The most common means of obtaining chorionic villi by CVS is with a transvaginal approach by insertion of a small flexible catheter into the uterus through the cervix (with positioning that is similar to undergoing a pap smear). CVS can also be performed using a transabdominal approach for sampling chorionic villi by insertion of a small needle into the lower abdomen and uterus similar to the procedure performed for genetic amniocentesis.  A local anesthetic is generally used for the transabdominal procedure. Both techniques use ultrasound guidance for chorionic villi collection. The tissue sample is sent to a laboratory for evaluation of karyotype (chromosomes) and any other indicated genetic testing. 

When are the CVS results available? 

Final results of the chromosome testing following tissue culture are generally received within 10-12 days of the procedure.  Results of testing for other genetic diseases may take a longer period of time and generally are based on the type of testing requested.  In some cases preliminary results may be obtained earlier following direct karyotyping of uncultured chorionic villi (or trophoblasts), or using a specialized laboratory technique such as fluorescent in situ hybridization (FISH).

What are the advantages of CVS testing as compared to amniocentesis? 

The principle advantage of CVS testing is the availability of early diagnostic testing.  In general the results are expected to be finalized in the late first or early second trimester.  With some genetic disorders early testing can be important in determining duration of or need for continued medical therapy.  Receiving results earlier in pregnancy also provides for greater patient privacy with regards to decision-making when the test results are abnormal.

What are the risks of CVS testing? 

The procedure related pregnancy loss risk of CVS testing is less than 1%.  Chromosomal mosaicism is found in approximately 1% of CVS samples and generally requires follow-up amniocentesis to confirm the presence or absence of mosaicism in the fetus.