Differences Between Chorionic Villus Sampling and Amniocentesis


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Antenatal testing genetic testing techniques are an invaluable method of determining the health and safety of an unborn baby, allowing for a diagnosis of conditions like Fragile X and Down’s Syndrome weeks before birth. The two main procedures used for antenatal testing are chorionic villus sampling (CVS) and amniocentesis. This article discusses the similarities and differences between these two powerful diagnostic tools.

Similarities between CVS and amniocentesis

Both CVS and amniocentesis are means by which you and your doctors can find out whether or not an unborn child is carrying genetic defects that will ultimately result in a severe illness. Both techniques operate on the same approximate principle of extracting foetal cells from the womb without causing injury to either mother or child.

Unlike other genetic tests, CVS and amniocentesis test a child directly as opposed to his or her parents, meaning that more concrete information about the health of a child can be provided. Tests performed on parents can give an approximate idea of what the chances are that a child might inherit particular genetic illnesses. CVS and amniocentesis are actually good follow up tests that can determine whether or not a child has inherited a particular genetic illness.

Differences between CVS and amniocentesis

CVS and amniocentesis can only be performed at specific times during a pregnancy. CVS is usually performed at or around 12 weeks of pregnancy (between the 10th and 14th week), while amniocentesis can only be performed between the 15th and around the 20th week. This is because while the two tests are fundamentally similar, they are performed in distinctly different ways.

Amniocentesis involves extracting some of the fluid which protects an unborn child (amniotic fluid), and is done by passing a needle through the abdomen. CVS actually takes out a small sample of the placenta, which is a structure allowing for the exchange of materials between maternal and foetal blood. CVS can be done either through the abdomen or through the opening of the womb, the cervix.

CVS actually has a slightly higher risk of miscarriage than amniocentesis. While amniocentesis is currently thought to have a miscarriage rate of around 0.5-1%, while CVS is thought to have a chance of between 1 and 2%.

Whether you receive CVS or amniocentesis is dependent on when you are having a genetic test done. If it is after the 10 week mark and before the 15 week point, then it will be CVS, while after 15 weeks but before 21 weeks it will be amniocentesis.


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