Some patients have the sampling done through the vagina and cervix.
Most patients have the sampling done through the abdominal wall. For both types of sampling, you will lie on your back on an examination table and the doctor will use ultrasound to locate the fetus and the placenta. If the sampling will be done through the vagina and cervix, you will need to have your feet in rests with your knees bent up for the procedure, as you would for a pelvic examination. A long tube, much narrower than a straw, is inserted through the cervix and moved forward while your doctor watches on the ultrasound until it is next to the fetal side of the placenta. A small sample of the lining around the fetus is then pulled into the tube for testing.