Robertson, Audra (September 19, 2006). "Medical Encyclopedia: Chorionic Villus Sampling." Medline Plus. Retrieved February 15, 2008, from http://www.nlm.nih.gov/medlineplus/ency/article/003406.htm

I found this article to be very informative on the procedure of chorionic villus sampling. Depending on where the placenta is located, CVS may be performed either transcervical (through the cervix) or transabdominal (through the abdomen). Both of these techniques are aided by ultrasound guidance. Doctors suggest the patient drink fluids the morning of the procedure and abstain from urinating. Having a full bladder allows for a more sufficient visualization from which a sample is taken. Patients have reported pain similar to a pap smear and menstrual cramping. A small amount of bleeding may occur after the procedure. This procedure is a way of detecting over two hundred genetic defects including Down syndrome, Hemoglobinopathies, and Tay-Sachs disease. Fetal loss only occurs about two percent of the time but there are a number of possible complications. Some of which include; rupture of the amniotic membrane, spontaneous abortion, infection, bleeding, Rh incompatibility in the mother, or contamination of the sample with maternal cells. Two to four days after the CVS, a follow-up ultrasound is usually scheduled to ensure that the fetus survived the procedure. It is suggested that if there are any signs of excessive bleeding, vaginal discharge, fever, or miscarriage that they be reported to you health care provider as soon as possible.