Genetics Northern California

Chorionic Villus Sampling

CVS is a prenatal diagnostic procedure done to identify chromosome abnormalities. This procedure is usually done between 10 weeks and 13 weeks 6 days of pregnancy.Ultrasound guidance is used during the entire procedure. The test involves removing and analyzing a sample of the developing placenta (the chorionic villi). The placental cells contain fetal chromosomes, which are evaluated in the laboratory.


CVS can be done in two different ways, either through the cervix (transcervicall) or through your lower belly (transabdominal). The doctor doing the procedure decides which method is best based on the location of the placenta and the anatomy of the woman having the procedure.


 Here is a brief, easy-to-read fact sheet about CVS:      Chorionic Villus Sampling.

Transabdominal CVS is done by inserting a thin needle through the woman's abdominal wall into the uterus and removing a small sample of the placental tissue (chorionic villi).

Transcervical CVS is done by inserting a thin flexible tube (a catheter) through the vagina and cervix into the uterus and removing a small sample of the placental tissue (chorionic villi). 

Risks: The risk for miscarriage due to the CVS procedure is 1 in 500 or less.

Results:A genetic counselor will call you with your results as soon as they are available. Results from CVS are usually available within 14 days. The results will accurately tell whether or not the baby has a chromosome abnormality, such as Down syndrome or trisomy 18. The result is unclear in about 3-5% of CVS tests. Further testing may be recommended. 

CVS does not detect neural tube defects (NTDs) since the amniotic fluid containing AFP is not sampled. However, AFP can be measured in the woman's blood between 15 and 20 weeks of pregnancy by a simple blood test. A follow-up ultrasound or amniocentesis is offered if the level of AFP is elevated.

Last reviewed:    December 2016

Reviewed by:      Kaiser Permanente Genetics Department