• 1st Trimester Genetic Risk Assessment
• Maternal Screening
• Chorionic Villous Sampling
• Genetic Amniocentesis
• Cystic Fibrosis Carrier Screening
• Integrated Prenatal Screening

Chorionic Villous Sampling

Chorionic villous sampling (CVS) is a form of prenatal diagnosis that is performed during the first trimester of pregnancy.  Chorionic villous sampling provides the earliest diagnosis of problems in fetal development.  It can be done between ten and twelve weeks of gestation according to ultrasound dating while the amniocentesis is typically performed after 15 weeks of pregnancy. 

The CVS can be performed in one of two ways; transcervically, by inserting a thin hollow tube (catheter) through the vagina and the cervix into the uterine cavity or transvaginally; by inserting a needle through the abdomen (similar to an amniocentesis). The tip of the catheter needle is then guided by ultrasound to the tissue that will become the placenta (the villi) and a small amount of tissue is withdrawn.  Most women who have had a CVS say the procedure causes little discomfort because the catheter is so thin.

The decision about which way to do the CVS is up to the physician at the time of the procedure and is based on placental location, position of the uterus, and gestational age.

Since part of the placenta, the villi, is of fetal origin these cells reflect the genetic make up of the baby.  The villi can be cultured (grown) and tested for many, but not all, genetic disorders.  Most commonly, CVS is performed to test for chromosome abnormalities like Down syndrome.  When indicated, other biochemical or DNA testing may be available; e.g., Tay-Sachs testing. 

Measurement of the alpha-fetoprotein routinely performed on amniotic fluid samples to detect openings in the spine (neural tube defects) is not possible with CVS.  Thus, CVS may not be the best option for people with an increased risk to have a baby with spina bifida. 

CVS has a higher spontaneous abortion rate than amniocentesis. At the University of Washington Medical Center, our loss rate is 1-2%, similar to the national average.

Results from a CVS take approximately two to three weeks to obtain. In the event of an abnormal result decisions regarding the management of the pregnancy can be made early in the second trimester. 

Genetic counseling is provided to fully explain all prenatal testing options, including the benefits and limitations of CVS and amniocentesis.  A detailed family history is taken and genetic risks are assessed based on family history, age and other screening factors.  Early genetic counseling and risk assessment is desirable to make the most appropriate choices for your pregnancy. 

REMINDER:  We will need the following information before we can perform a CVS. 

• Vaginal cultures for (transcervical CVS only): gonorrhea, chlamydia, beta-streptococcus, yeast and gardnerella 
• Gestational age by ultrasound: the CVS procedure can ONLY be done between 10 and 12 weeks 
• Blood type including Rh status

A VERY full bladder is required for a CVS.  Please plan on bringing one quart of water to drink within the hour before the CVS appointment. 

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Last Updated:
4/12/07