CHORIONIC VILLUS SAMPLING (CVS)

CVS is usually performed between 10 and 12 weeks from the first day of the last menstrual period.  CVS is used to collect a sample of chorionic villi, which are small pieces of placental tissue.  Because the placenta forms from the same tissue as the fetus, chromosome analysis of the chorionic villi cells reflects the chromosomal state of the fetus.
 
CVS is performed by one of two techniques, depending on where the placenta is located in the uterus.  Prior to CVS, an ultrasound is performed to determine the best method for sampling.  In transcervical CVS, a thin catheter is inserted through the vagina and cervix to obtain the placental tissue.  Transabdominal CVS is similar to amniocentesis and is performed by inserting a thin needle through the abdomen and into the uterus to collect the placental tissue.  Some cramping or discomfort may be experienced during either procedure. 

Once a sample is obtained, cells from the chorionic villi are grown in the laboratory and their chromosomes analyzed under the microscope.  Results are typically available within two week.  CVS can test for certain genetic disorders such as cystic fibrosis, sickle cell anemia, and Tay-Sachs disease, if these tests are specifically ordered.

If the mother is Rh negative and the father is Rh positive, the mother will receive an Rh immune globulin (RhoGAM) injection after the procedure to prevent Rh antibodies from forming. 

Limitations: Although CVS can detect chromosome abnormalities, there can be no guarantee of a perfect baby.  CVS cannot detect all causes of birth defects, genetic disease, and/or mental retardation. Unlike amniocentesis, CVS cannot test for neural tube defects such as spina bifida.  Therefore AFP testing of the mother's blood at 16 weeks as well as a detailed ultrasound examination at 18-20 weeks gestation are recommended.

Risk: There is less than a one in 100 (1%) risk for complications from CVS that could result in miscarriage.  Approximately 1% of the time, a second procedure is recommended after CVS.  Occasionally there is a mosaic result (detection of more than one cell line in the placenta) and amniocentesis is recommended to clarify the chromosomal state of the fetus.  The cells may fail to grow in culture. 

Aftercare:  It is recommended that physical activity be limited for 24 hours following the procedure.  Avoid:

• heavy lifting (greater than 10 pounds)
• exercise
• sexual activity
• standing for long periods of time
• physically strenuous activities

Call your obstetrician immediately if you experience:

• bleeding or leaking fluid from the vagina (some vaginal spotting may occur after the procedure.  If the spotting does not resolve within three days, call your obstetrician)
• severe cramping (mild cramping, like menstrual cramps, is normal on the day of the procedure)
• signs of infection, such as fever or chills
  
  
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