Chorionic Villus Sampling

1 What is a Chorionic Villus Sampling?

Chorionic villus sampling (CVS) is a prenatal test in which a sample of chorionic villi is extracted from the placenta for testing. This sample can either be taken through the cervix (transcervical) or the abdominal wall (transabdominal).

During the period of pregnancy, the placenta provides oxygen and nutrients to the developing baby and removes waste products from the baby's blood. The Chorionic villi are wispy projections of placental tissue that share the baby's genetic makeup.

Chorionic villus sampling is normally performed the tenth and thirteenth week of pregnancy, earlier than other prenatal diagnostic tests like amniocentesis.

Chorionic villus sampling can be used to reveal whether the baby has a chromosomal condition, such as Down's syndrome. Chorionic villus sampling can also be using for testing for other genetic conditions, such as cystic fibrosis.

Although Chorionic villus sampling can provide useful information about your baby's health, it is vital to understand the risks and be prepared for the possible results.

2 Reasons for Procedure

Here are the most common reasons to undergo a chorionic villus sampling.

Chorionic villus sampling can provide vital information about your baby's genetic makeup.

In general, chorionic sampling is given when the tests results might have a significant impact on the management of the pregnancy or you have the desire to continue the pregnancy.

Chorionic villus testing can be performed between week 10 and 13 of pregnancy.

You may consider chorionic villus sampling for the following reasons:

  • You had positive results from a prenatal screening test. If the results of a screening test, such as the first-trimester screen or prenatal cell-free DNA screening are positive or worry-inducing, you might opt for chorionic villus sampling to make a confirmation or rule out a diagnosis.
  • You had a chromosomal condition in a previous pregnancy. If your child in a previous pregnancy was affected by Down's syndrome or another chromosomal condition, the current pregnancy is at a higher risk as well.
  • You are 35 and older. Babies born to women who are 35 or older have a higher risk of chromosomal conditions, such as Down's syndrome.
  • You have a family history of a specific genetic condition, or your partner is a known carrier of a certain genetic condition. Apart from being used in the identification of Down's syndrome, chorionic villus sampling can also be used to diagnose many other genetic conditions, including single-gene disorders like cystic fibrosis and Tay-Sachs.

Chorionic villus sampling cannot detect certain birth defects, such as neural tube defects. If neural tube defects are a concern, an ultrasound or genetic amniocentesis might be recommended instead.

Your health care provider might caution against transcervical chorionic villus sampling, which is done through the vagina, if you have the following:

  • An active cervical or vaginal infection, such as herpes.
  • Vaginal bleeding or spotting in the previous two weeks.
  • An inaccessible placenta, as a result of a tilted uterus or noncancerous growths in the lower part of your uterus or noncancerous growths in the lower section of your uterus (uterine fibroids).

Only rarely can your health care provider caution against transabdominal chorionic villus sampling, which is done through the abdominal wall, if:

  • Your uterus is tilted backward and your placenta is located at the back of your uterus.
  • Rhesus factor, which is an inherited trait that refers to a specific protein that is found on the surface of red blood cells, matters too.

Your health care provider might caution against both types of chorionic villus sampling if you are Rh negative, your baby is Rh positive and your body has already begun to produce Rh antibodies.

Bleeding caused by the procedure could increase your antibody response and cause pregnancy complications.

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3 Potential Risks

The following risks are associated with chorionic villus sampling:

  • Miscarriage: The risk of miscarriage after chorionic villus sampling is about three times that associated with transabdominal second-trimester amniocentesis, around 7 percent. The risk of miscarriage might increase if the baby smaller than normal for his or her gestational age.
  • Rh sensitization: Chorionic villus sampling might lead to some of the baby’s blood cells to enter your bloodstream. If you have Rh negative blood and have not developed antibodies to Rh positive blood, you will be given an injection of a blood product called Rh immune globulin after chronic villus sampling, this will prevent your body from producing Rh antibodies that have the ability to cross the placenta and damage the baby's red blood cells. A blood test can detect if you have begun to produce the antibodies.
  • Infection: In very rare cases, chronic villus sampling might trigger a uterine infection.

Some older studies suggested that chorionic villus sampling might cause defects in the baby's fingers or toes. However, the risk appears to be a concern only if the procedure is done before week 10 of pregnancy.

Remember, chorionic villus sampling is typically given when the test results might have a significant impact on the management of the pregnancy.

Ultimately, the decision to have a chorionic villus sampling is in your hands. Your health care provider and genetic counselor can help you weigh all the factors in the decision.

4 Preparing for your Procedure

Your bladder might be required to be full for chorionic villus sampling. In order to prepare, drink plenty of fluids before your appointment.

Your health care provider will explain the procedure and ask you to sign a consent form before the procedure begins. Consider asking someone to accompany you to the appointment for emotional support or to drive you home afterwards.

5 What to Expect

Here’s what you can expect before, during, and after your procedure. Chorionic villus sampling is usually done in an outpatient facility or health care provider's center.

During the procedure

  • To start with, your health care will use an ultrasound to determine your baby's gestational and the position of the placenta.
  • You will lie on an exam table and then lift your shirt in order to expose your abdomen.
  • Your health care provider will apply a special gel to your abdomen, and then use a small device known as a transducer to show the position of your baby on a monitor. 
  • Next, your health care provider will use the ultrasound image as a guide to take a sample of tissue from the placenta while you lie still. This can be done through your cervix (transcervical) or through your abdominal wall (transabdominal). 

Transcervical chorionic villus sampling

  • After cleansing your vagina and cervix with an antiseptic, your health care provider will open your vagina with a speculum and insert a thin, hollow tube through your cervix.
  • When the catheter reaches the placenta, gentle suction will be used to remove a small sample of tissue. You might feel cramping while the tissue sample is being removed. 

Transabdominal chorionic villus sampling

  • After cleansing your abdomen with an antiseptic, your health care provider will proceed to insert a long, thin needle through our abdominal wall and into your uterus. You might notice a stinging feeling as the needle enters your skin, and you might feel cramping as the needle enters the uterus.
  • The tissue sample from the placenta will be withdrawn into a syringe, and the needle will be removed. If your health care provider is not able to remove an adequate amount of tissue on the first try, the procedure might be repeated. 

After the procedure

After the tissue sample has been removed, your health care provider will monitor the heart rate of your baby. You might experience a small amount of vaginal bleeding immediately after the procedure.

Your health care provider might schedule an ultrasound a couple of days after chorionic villus sampling to check on your baby.

You can return to your normal daily routine after the procedure. However, you might consider avoiding any strenuous exercise and sexual activity for a day.

Meanwhile, the sample of tissue will be analyzed in a lab. Results might take a few days or a couple of weeks, this depends on the complexity of the lab analysis.

Contact your health care provider if you experience the following:

  • Heavy bleeding
  • A fever
  • Fluid leaking from your vagina
  • Uterine contractions

6 Procedure Results

Your health care provider or genetic counselor will assist you in understanding your chorionic villus sampling results. Occasionally, test results are not clear and amniocentesis, another prenatal diagnostic test, will be needed for the clarification of the diagnosis.

With chorionic villus sampling, there is a rare chance of a false-positive test when the test is positive, but no disease exists.

It is also important to always keep in mind that chorionic villus sampling cannot identify all possible birth defects, including spina bifida and other neural tube defects.

If chorionic villus sampling shows that your baby has a chromosomal genetic disorder that does not have a treatment, you might be faced with wrenching decisions, such as whether to continue the pregnancy. Seek support from your health care team and your family during this difficult time.

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