This test, just like amniocentesis analyses chromosomes to check for anomalies, although the procedure used to obtain the genetic material is different.  

What is chorionic villus sampling

This test requires obtaining a sample of chorionic villus to analyze the baby’s chromosomes. Chorionic villi are the tiny fingerlike projections that attach the amniotic sac to the uterus. These villi have some of the baby’s cells, which are then cultured to obtain a sample of the baby’s chromosomes.  

Although it is a test similar to amniocentesis, chorionic villus sampling is done between weeks 10 and 12 of pregnancy. That is, it can be carried out five weeks before amniocentesis. Also, the results come back earlier.  

This test can establish whether there is a problem in the chromosomes, such as Down’s syndrome and it can also look for specific genes such as that for cystic fibrosis, if there is a family history of that. This test does not detect other problems such as spina bifida.  

How the test is carried out

The villus sample may be obtained in two ways: with a procedure similar to a gynecological exam or with a procedure similar to the amniocentesis.  

In the first case, your doctor will disinfect the external and internal parts of your vagina. She will then introduce a very small tube and will vacuum the villi. It is a very similar procedure to when the doctor takes a sample of your cervix in order to carry out a pap smear.  

The other procedure is through the belly. This entails inserting a needle in your belly and extracting a small sample of villi through the needle.

Potential risks

This procedure has a higher risk of miscarriage than amniocentesis; there is one miscarriage for every 100 to 200 tests. There is a risk for the babies of mothers who have undergone this test to have defects in their extremities or the jaw. However, this only happens in one out of every 1000 to 3000 pregnancies. When the test is done after the tenth week of pregnancy, the risks are even lower.  

Chorionic villus testing is usually done when there is a history of a previous baby with chromosomal problems or if there is a family history of a certain genetic disease, such as cycstic fibrosis, and there is a probability of the baby having one of those genes.  

In the event that you decide to undergo this test, make sure that the doctor or technician who is going to carry it out is experienced, to minimize the risks. If a villus sample is obtained on the first attempt, the test won’t have to be repeated and therefore the risks will decrease.  

When to call the doctor

This test does not puncture the amniotic sac; it only takes villi from the exterior. After the procedure it is normal to spot a little or to feel discomfort. However, if you are leaking fluid (it could be amniotic fluid) or if you feel contractions or more pain, you should call your doctor immediately or go to the hospital, to make sure you are not in preterm labor.