The chorionic villus sampling (CVS) procedure involves obtaining a sample of the chorion or placenta. It is an outpatient procedure performed between the 10th and 12th week after the first day of the last menstrual period. The procedure can be done through the cervix with a thin plastic tube, or it can be done through the mother's abdomen with a needle, depending on the location of the placenta. It is done under ultrasound guidance.

The advantage of CVS is the ability to obtain genetic information about the fetus in the first trimester of pregnancy. CVS cannot provide any information about neural tube defects. If you are at risk for a neural tube defect, amniocentesis, rather than CVS will be recommended.

Any medical procedure has potential risks. The risks of CVS include bleeding, infection, and miscarriage. The miscarriage rate at 10-12 weeks without any procedure is about 3%. In patients who undergo CVS, the miscarriage rate increases less than 1%. About 1/3 of patients who have CVS will experience some bleeding after the procedure. This is usually just spotting and stops in a few days. Infections are very rare but can be serious if not treated. Though CVS is an accurate test, it occasionally yields false abnormal results that require later amniocentesis for interpretation.


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