Amniocentesis is highly recommended for all pregnant females over the age of 35. This procedure is also highly recommended for all couples that have a known genetically related disease in their family histories. For best results, this procedure should be done by a Perinatalogist. This is an Ob/Gyn who specializes in high-risk pregnancies.

Both amniocentesis and CVS (chorionic villus sampling) are procedures to test the chromosomes of the developing baby. Chromosomes contain DNA, which is a genetic code that determines things like eye color, skin type and predisposition to certain inherited diseases. Not only is the information coded for by the DNA on the chromosomes important, but the absolute number of chromosomes is also important.

Normally, an individual has 46 chromosomes. You inherit 23 chromosomes from your mother and 23 from your father. Rarely, during the process of formation of eggs and sperm, a chromosome will either be lost (this is called "monosomy") or gained (this is called "trisomy"). One of the most common trisomies is trisomy 21, which means that the fetus has three copies of chromosome 21, instead of the usual two copies. This is commonly referred to as Down’s syndrome.

Amniocentesis and CVS can both test for the structure and number of chromosomes. Women who are 35 years of age or older are offered amniocentesis or CVS specifically to test for chromosomal number, because the risk of problems with chromosomal number are increased in this age group. Amniocentesis and CVS are also performed in patients of any age when they are known to be at risk of having a child with a genetic disorder, such as cystic fibrosis or sickle cell disease.


Amniocentesis is typically performed at 15 to 18 weeks gestation and is done by inserting a small needle through the mother’s abdomen and uterus into the amniotic fluid surrounding the baby. A small amount of amniotic fluid is removed for analysis. The needle is associated with minor discomfort, but most women do not find the procedure to be inordinately painful.

CVS is usually performed at 10 to 12 weeks gestation and can be done one of two ways:

  1. A small flexible plastic catheter can be inserted through the cervix into the developing placenta. A small amount of tissue is then removed for testing. This is known as a transcervical CVS. 
  2. A second way to perform CVS is by inserting a small needle through the mother’s abdomen and uterus, much like amniocentesis, but the needle goes into the placenta rather than the amniotic fluid. This is known as a transabdominal CVS. The decision of which method to use is based on the location of the placenta. Like amniocentesis, neither of the two ways to perform a CVS are particularly painful. The results of both tests take about 1 to 2 weeks to complete and are highly accurate.


What are the risks associated with these procedures? Any "invasive" diagnostic test during pregnancy carries a small risk of miscarriage. For amniocentesis and CVS, that risk is in the range of 0 to 1 percent. So, even though this risk is small, each woman must decide for herself if the information she will receive from the test is worth the small risk associated with it.

Another common question is, "Can these procedures damage the baby?" Both amniocentesis and CVS are done with the assistance of ultrasound to enable the person performing the procedure to accurately place the needle or catheter away from the baby. Using this approach, it is exceedingly unlikely that either of these procedures can cause damage to the developing baby.

This article is reproduced from the FamilyFun web site.