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Definition

What is choronic villus sampling?

Chorionic Villus Sampling (CVS) is a test done in early pregnancy to check for certain problems with the fetus. This is generally done when you or the father of the fetus have a hereditary disease in the family. This test can be done when you are pregnant at the age of over 35 years — when you are over 35 the risk of developing defects increases. The genetic material in chorionic villus cells is the same as in baby cells. During CVS, a sample of chorionic villus cells is taken for examination. The chorionic villus cells are examined to determine the problem. This procedure is often performed during the last 10 and 12 weeks.

The chorionic villus sample is taken using a thin flexible tube (catheter) that is inserted into the placenta. The sample can also be taken through a long, thin needle that is inserted through the stomach into the placenta. Ultrasound is used to guide a catheter or needle to the right place to collect the sample.

If your family has a history of certain diseases, CVS can be used to find genetic disorders. This test can also be used to detect chromosomal birth defects. CVS cannot be used to see the development and growth of a baby.

Chorionic villus sampling can be done early in pregnancy (at 10 to 12 weeks). This allows you to know your baby's health and make a decision beforehand whether to continue or end the pregnancy. Results from CVS may become available sooner than results from amniocentesis.

When should I undergo choronic villus sampling?

CVS is not routinely recommended during pregnancy. This test is only used if the results of previous tests or your medical history indicate that your baby is at high risk of developing a genetic disorder. Some of the conditions that can be detected via CVS include:

• chromosomal conditions, such as disorders that generally cause some degree of learning disability and various characteristic physical features, or, disorders that can cause developmental disabilities
• genetic disorders, such as disorders that make body secretions thick and sticky, inhibiting the function of certain organs
• disorders of the musculoskeletal system such as Duchenne, a genetic disorder that causes progressive muscle weakness and disability
• a blood disorder such as a condition that affects your body's ability to produce red blood cells, or, that affects how red blood cells carry oxygen around your body
• metabolic disorders such as antitrypsin deficiency, in which your body cannot produce the alpha-1 antitrypsin protein, or, where your body cannot produce the enzyme phenylalanine hydroxylase
• Mental health conditions such as fragile X syndrome, are conditions that can affect your appearance, intelligence and behavior

Like the conditions above, several other, lesser known conditions may also be detected with CVS. If it is possible that your fetus has a condition that can be detected by CVS, the specialists involved in carrying out the test will discuss it with you. You will be given advice regarding the risks of this procedure and information that can help you deal with the test results.

If the identified condition cannot be cured / treated, or if it causes severe disability in the baby, the parent may decide to terminate. However, if the parents decide to continue the pregnancy, CVS will provide early notification regarding the condition, so that it can give both parents time to prepare for the challenges that will be faced in the future.

Precautions & warnings

What should I know before undergoing choronic villus sampling?

CVS cannot detect neural tube defects. This is a birth defect that affects the brain and spinal cord. Normal results from chorionic villus sampling (CVS) do not guarantee that your baby will be healthy.

Amniocentesis (which is more common in late pregnancy than CVS) can also be used to check for other diseases of the fetus, such as neural tube defects. If CVS does not show clear results, then amniocentesis may be necessary. The results of CVS may vary depending on the method of sampling.

If you have a vaginal infection, an abdominal procedure will be used instead of a vaginal procedure. CVS causes bleeding that can lead to mixing of your and your baby's blood. If you have Rh-negative blood, you will be given an Rh immunoglobulin vaccine (such as RhoGAM) to prevent things that could harm your baby if he has Rh-positive blood.

Process

What should I do before undergoing choronic villus sampling?

It may take a full bladder for chorionic villus sampling, so drink plenty of fluids before your CVS schedule. Depending on the position of the placenta, you may be asked to empty your bladder before the procedure. Your doctor may ask you to sign a consent form before the procedure begins. Consider having someone accompany you on exam day for emotional support or to drive you home afterward.

How is the choronic villus sampling process?

Chorionic villus sampling is usually performed by a perinatologist in a doctor's office or hospital. You don't need to spend the night in the hospital unless there are problems during the procedure. There are two types of CVS that can be performed, transabdominal (through the stomach) chorionic villus sampling or transcervical (through the cervix) chorionic villus. The choice may depend on where the fetus and placenta are in the uterus.

Through the stomach (transabdominal)

You will lie on your back on the examination table with your naked stomach. Gel will be applied to your abdomen for use with the ultrasound unit. An ultrasound device (transducer) that can provide and capture sound waves will be run on your stomach. The reflected sound waves are sent to a computer to display a photo of the uterus, fetus and placenta on a screen. Your doctor or ultrasound technician will look at images to direct the needle used to collect a sample of the chorionic villus. Your baby's heart rate can also be checked during this procedure using ultrasound. For more details, see the topic Fetal Ultrasound.

The area of ​​your skin to be injected is cleaned with alcohol and anesthetized with a drug. Your doctor then injects a long, thin needle through your stomach and uterus leading to the placenta and collects a sample of chorionic villus cells.

After the sample is collected, your doctor will listen to the baby's heartbeat and check your blood pressure, pulse, and breathing.

Through the cervix (transcervical)

You will be asked to remove your clothes from the waist down and wrap the covering around your waist. Then you will lie on your back on an examination table with your feet raised and assisted by foot ramps. This allows the doctor to see your genital area.

Your doctor will place an instrument with a curved side (speculum) into your vagina. The speculum carefully expands the vaginal walls separately, exposing the inside of the vagina and cervix. The cervix will be cleaned with a special soap.

An ultrasound will be used to help the doctor guide the catheter through your cervix to the placenta. An ultrasound device (transducer) that delivers and captures sound waves will be run on your stomach. The reflected sound waves are sent to a computer to display images of the uterus, your baby, and the placenta on a screen. Your baby's heart rate can also be checked during the procedure using ultrasound. When the catheter is properly placed, a sample of chorionic villus cells will be collected.

After the sample is collected, your doctor can listen to the baby's heartbeat and check your blood pressure, pulse, and breathing.

What should I do after undergoing choronic villus sampling?

After the tissue sample is removed, the doctor will use an ultrasound to monitor the baby's heart rate. You may experience some vaginal bleeding after the procedure. The tissue sample will be analyzed in a laboratory. Results may take several days or several weeks, depending on the complexity of the laboratory analysis.

If you have questions related to this test process, please consult your doctor for a better understanding.

Explanation of the Test Results

What do my test results mean?

The cells from your baby are looked at carefully by checking to see if the amount and arrangement of the genetic material (chromosomes) is correct and indicates the presence of a genetic disease. There are usually 46 chromosomes in each cell, arranged in 23 pairs. The chromosomes can also tell the gender of your baby. It can take 1 to 2 weeks before the CVS results come out.

Normal:

No abnormalities were found in the genetic material of the chorionic villus cells.

Abnormal:

The discovery of abnormalities in the genetic material of the chorionic villus cells.