Amniocentesis and CVS - A Comparison

Introduction

Prenatal tests are some tests done before the birth of the child or during pregnancy. It is a method to know any abnormalities in an unborn child. The two tests done are amniocentesis and chorionic villus sampling (CVS). These tests help to diagnose any genetic abnormalities in the unborn fetus. Knowing about some defects before birth can help to prepare the parents. Some conditions might have treatment while the baby is still unborn. Others might require special care and medical attention immediately after the child's birth. If required, the parents can decide to discontinue the pregnancy.

What Is Amniocentesis?

Amniocentesis is a prenatal test to check if the baby has any chromosomal or genetic abnormalities. A sample of amniotic fluid is removed and tested. The fluid that surrounds the baby in the uterus is called amniotic fluid. However, the test is not done in all pregnant women. It is done in women with a higher risk of genetic abnormalities. However, the woman will have the right to deny it if she wishes to.

How Is Amniocentesis Done?

An amniocentesis is done within the fifteenth to twenty-first week of pregnancy. The test can be done earlier. However, this increases the risk and complications of the procedure. A long and thin needle is inserted into the pregnant woman's abdomen, guided by an ultrasound. The needle is pierced through the amniotic sac, and some amniotic fluid is extracted. The test may take around ten minutes. Most women who undergo the procedure describe the procedure as uncomfortable rather than painful.

The first result of the test will be received within three days after the procedure. It gives information if the baby has conditions like Down's syndrome (a genetic disorder caused by an extra chromosome of 21), Edwards' syndrome (a genetic disability caused by an extra chromosome 18), or Patau's syndrome (a genetic condition caused by an extra chromosome 13). However, if testing for rare conditions, it would take three weeks or more to get the results. The results should be explained to the parents if they show chromosomal abnormalities.

What Are the Risks Associated With Amniocentesis?

The associated risks should be discussed with the pregnant woman before the procedure. Miscarriage is one of the main risks associated with amniocentesis. (Miscarriage is the loss of pregnancy before twenty-three weeks of pregnancy). Studies show that about one in two hundred women with amniocentesis have had an abortion. The risk of complications is higher if the procedure is done before fifteen weeks. Hence, it is usually done after fifteen weeks of pregnancy. The other risks can include:

1. Infection.

2. The requirement to repeat the procedure is due to insufficient sample collection or needing accurate results with the sample taken first.

An alternative to amniocentesis is chorionic villus sampling (CVS).

What Is Chorionic Villus Sampling?

Chorionic Villus Sampling (CVS) is another prenatal test. It is very accurate and can detect abnormalities in the unborn fetus. This procedure can also do gender determination. A small sample of cells is taken from the placenta in this procedure. The placenta is an organ that develops during pregnancy. It provides nourishment to the fetus. The cells removed are called 'chorionic villi.' They are cells formed from the fertilized egg and have the same genetic constitution as the fetus.

How Is Chorionic Villus Sampling Done?

The procedure might not be painful but can cause some discomfort. The test is done in two different ways.

1. Transcervical (Through the Vagina): A speculum is inserted into the vagina. A speculum is a smooth instrument shaped like a duck's bill. It is also used in a Pap smear. It helps to widen the walls of the vagina. A thin plastic tube is inserted through the vagina with guidance from the ultrasound. It is guided to the placenta to remove a small sample from it.

2. Transabdominal (Through the Abdomen): A thin needle is inserted into the placenta through the abdomen guided by the ultrasound to remove a few cells. Local anesthesia might be given to reduce the discomfort.

For multiple pregnancies (twins, triplets, etc.), each fetus might require a separate CVS test. A second test might be optional in most cases. The test results require a few weeks for rare conditions, while simpler conditions may be received in a few days.

What Is the Difference Between Chorionic Villus Sampling and Amniocentesis?

Both the procedures, chorionic villus sampling and amniocentesis, are done in the prenatal period to detect any abnormalities in the fetus. But they are done at two different periods during pregnancy. Generally, CVS testing is done at ten to thirteen weeks, while amniocentesis is done after fifteen weeks. There are differences in what the tests are done for. Amniocentesis can be used to test for defects in the neural tube. The neural tube is the structure that gives rise to the brain and the spinal cord. An example of a defect in the neural tube is the spina bifida. On the other hand, CVS cannot diagnose these conditions.

Why Is Amniocentesis a More Widely Used Test Than CVS?

Most recent studies show that CVS and amniocentesis have low to no increased risk of pregnancy loss. A study published by a leading journal (Salomon et al., Ultrasound in Obstetrics and Gynecology) in 2019 shows that the risk of miscarriage associated with the procedure was 0.03 percent for amniocentesis, and no significant danger was connected to CVS procedures. This shows that CVS is relatively safe during pregnancy and can be done early. However, CVS cannot detect some conditions. They can include:

• Defects in the neural tube.

• Rh compatibility (when the mother is RH negative, and the baby is Rh positive).

The risks associated with CVS are slightly higher than amniocentesis. Hence, amniocentesis is generally more widely used than CVS.

Conclusion

Prenatal tests are done to check if the unborn baby has any defects. Amniocentesis and chronic villus sampling are two tests done to check the genetic abnormalities in the unborn baby. These tests help the parents to prepare themselves to accept the baby and for specialized treatment during pregnancy and immediately after birth.