Amniocentesis and CVS

Prior to an amniocentesis, you will meet with a Genetic Counselor to discuss the test thoroughly. After reading the following information, write down any questions that you may have and take them to your appointment.

The most common reasons why an amniocentesis is performed are:

During an amniocentesis a small amount (usually 2 tablespoons) of amniotic fluid that surrounds the fetus is removed. The amniotic fluid contains cells that have been shed by the fetus during normal development. These cells may then be used for chromosome tests and/or specific genetic tests. The fluid itself is tested for the level of alpha feto-protein (AFP) or for biochemical genetic disorders, if appropriate.

Amniocentesis is best done after 15 weeks and up to 23 weeks of pregnancy.  The amniocentesis procedure involves guiding a thin needle through the mother's abdomen and into the amniotic sac (see below). Ultrasound is used to determine the location of the fetus and the best place to withdraw the fluid.  The entire procedure is done under ultrasound guidance.

Most women do not report the amniocentesis procedure to be painful. It usually takes a minute or less to perform, and is commonly described as feeling like pressure rather than pain. Some women experience mild cramping for up to a few hours afterwards.

Because the needle must pass through the amniotic sac, there is a chance of the fluid leaking or the sac rupturing. As with all invasive procedures, there is also a chance that an infection may occur. Any of these complications may cause a miscarriage. The risk for miscarriage from an amniocentesis when performed by highly experienced physicians is approximately 1 in 400 (or 0.25%).

Examples of ultrasonography you may see used during your pregnancy.
Ultrasound information :-    Who, Why, When?
What happens during an ultrasound examination?
Can the scan show the gender of my baby?

CVS (Chorionic Villus Sampling)

Prior to chorionic villus sampling (CVS), you will meet with a Genetic Counselor to discuss the test. After reading the following information, write down any questions that you may have and take them to your appointment.

The most common reasons a CVS (Chorionic Villus Sampling) is performed are:

CVS is a specialized alternative test to amniocentesis. It involves removing a small amount of tissue called the chorionic villi, which is located on the outside of the fetal gestational sac and will later become the placenta. The chorion is a fetal tissue, and shares its genetic makeup with the fetus, not the mother. The chorion has many small, finger-like projections on its outer surface, and a few of these may easily be removed without disturbing the pregnancy. The chorionic villi cells may be used for chromosome analysis or other genetic testing. The chorionic villi cannot be used to test for open neural tube defects.

The CVS may be performed transabdominally by guiding a thin needle through the abdominal wall to the chorionic villi, then withdrawing a small amount of this tissue. (See below - A)  Occasionally, particularly if the thickest location of the villi is in the lower portion of the uterus, the CVS is performed transcervically by using a thin flexible plastic catheter (hollow tube) which is guided through the cervical opening, somewhat like having a Pap smear done. This catheter is then used to remove a small amount of the villi. (See below - B).

Most women do not report the CVS procedure to be painful. It usually takes a minute or two to perform, and is commonly described as feeling like pressure rather than pain. Some women experience mild cramping for up to a few hours afterwards or rarely experience light spotting that usually goes away within a day or two.

Because the procedure involves going inside the uterus, there is a small chance of bleeding or infection. Any of these complications may cause a miscarriage, this risk is said to be approximately 1 in 200 (0.5%).