Chorionic villus sampling (CVS) is a procedure that can be performed between the 10th and 12th week of pregnancy to test for chromosomal abnormalities and some inherited genetic diseases.  Deciding whether or not to have CVS usually depends upon your particular risk factors and your concerns, but the decision regarding genetic testing is entirely up to you.  CVS may not be able to be performed if you have an unusually shaped uterus, unusual fetal or placenta position or infection.  If CVS is not performed, another diagnostic procedure called amniocentesis, may be done about 4-6 weeks later.  


Many tests can be done on a chorionic villus sample.  Most patients have the test to make sure that the baby does not have a chromosome abnormality.  The most common chromosome abnormalities (Down syndrome and trisomy 18) account for about two-thirds of all the chromosome abnormalities that can be detected by CVS.  The standard laboratory testing detects over 99% of common chromosome abnormalities.  Most chromosome results are available within 7-10 days.  


In some patients who are carriers for genetic diseases, CVS can also be used to test them.  Examples include Tay Sachs disease, sickle cell disease and cystic fibrosis.   Tests for rare genetic diseases may take up to 5 weeks.   Unlike amniocentesis, CVS cannot be used to test for open neural tube defects, such as spina bifida and anencephaly.  Since the CVS procedure is done relatively early in the pregnancy, ultrasound evaluation of the fetal anatomy is limited.  It is recommended that the patient return in 4-6 weeks for a detailed anatomical ultrasound survey.


Although CVS is a routine procedure, it does have some risks including less than a 1/100 risk of miscarriage, infection, harm to the fetus (<1/3,000) or need to repeat the procedure due to inadequate specimen.  These risks are related to practitioner experience.  Our CVS practitioner, Dr. Janet Horenstein, has been performing CVS for over 15 years and is a designated provider for CVS through the State Prenatal program.

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