Medical Content Created by the Faculty of the
Harvard Medical School
There are two ways that your doctor can perform CVS. 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 lie on your back on an examination table and the doctor uses ultrasound to locate the fetus and the placenta.
If the sampling is to be done through the vagina and cervix, you place your feet in footrests and bend your knees up, as you would for a pelvic examination. A speculum (a device that looks like a duck-bill that can be opened and closed) is used to open the vagina so that your doctor can see inside. 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.
If the sampling is to be done through the abdominal wall, your lower abdomen is cleaned with an antibacterial soap. In some cases, the doctor uses a small needle to inject a numbing medicine just under the skin, so that you do not feel the sampling needle. (Because the sampling needle does not cause much more stinging than the numbing medicine itself, not every doctor includes this step.) A hollow needle several inches long is inserted through the skin and muscle of the abdomen and through the wall of the uterus, to the edge of the placenta. This needle is held in place as a guide needle. A narrower needle is then inserted through the first needle and is rotated and moved inward and outward a number of times while a sample is collected into an attached syringe.
The fetal heart tones and the mother's blood pressure and heart rate are checked at the beginning and end of the procedure. The whole procedure takes close to 30 minutes.