Chorionic villus sampling

What is chorionic villus sampling?

Chorionic villus sampling (CVS) refers to a prenatal test. It’s utilised to assess chromosomal abnormalities and other genetic problems. A tissue sample is taken from the placenta during the test and sent to a lab for analysis. The placenta refers to a structure in the womb that supplies blood and nutrients from the mother to the baby.

The chorionic villi refer to tiny projections of placental tissue that appear similar to fingers. They have genetic material similar to that of a baby. Testing may be performed for other genetic defects as well as disorders. This will rely on the family history and on the types of lab testing that are available at the procedure time.

CVS is generally conducted between the 10th and 12th weeks of pregnancy. Unlike amniocentesis (an alternative type of prenatal test), CVS does not offer information on neural tube defects like spina bifida. For this reason, a mother who has CVS also requires a follow-up blood test between 16 and 18 weeks of their pregnancy. This is to screen for defects related to neural tube.

CVS procedures are of two types, as described below:

Transcervical: A tube (catheter) is inserted through the cervix into the placenta to obtain the sample of tissue.

Transabdominal: A needle is inserted through the belly and uterus into the placenta to extract the tissue sample.

Need of chorionic villus sampling

Reasons that a woman might choose to have CVS comprise:

A history of a genetic disease, chromosomal abnormalities, or metabolic disorder in a previous child
Maternal age over 35 by the pregnancy due date
Probability of a sex-linked genetic disease
Previous ultrasound with abnormal results
Abnormal results from cell-free DNA test

Risks of chorionic villus sampling

Some risks of this procedure comprise:

Cramping, bleeding, or water breaking.
Infection
Spontaneous abortion
Premature labour
Limb defects in case of infants, a higher risk in CVS tests conducted prior to 9 weeks. This is unusual.
Women with twins or other multiples will require sampling from each placenta to study each baby.

How to get ready for chorionic villus sampling?

The medical professional will explain the procedure to the mother.
Mother will be asked to sign a consent form allowing healthcare providers permission to do the procedure.
Generally, there is no restriction on diet or activity before CVS.
Mother should inform healthcare provider if she is sensitive to any medications, iodine, latex and anaesthetic medicines (local and general).
The mother should inform the healthcare provider about all the medicines that she is taking. This comprises prescription and over-the-counter medicines, vitamins, herbs, and other supplements.
Mother should inform healthcare provider if she has a history of bleeding disorders or if she is taking any blood-thinning (anticoagulant) medications, aspirin, or any other medicines that may impact blood clotting. Mother may require stopping these medications prior to the procedure.
It's important for the mother to notify her healthcare provider if she has a negative Rh factor. During a CVS procedure, there's a chance that blood cells from both the mother and the baby could intermingle. This could result in Rh sensitization, causing the breakdown of the baby's red blood cells.
In majority of cases, prenatal blood tests will have found out if mother is Rh negative. Mother may be asked to provide these lab results before the procedure.
Mother may or may not be asked to have a full bladder right prior to the procedure. Depending on the position of the womb and placenta, a full or empty bladder may aid move the uterus into a better position for the procedure.

What happens during Chorionic villus sampling (CVS)?

A CVS procedure may be carried out on an outpatient basis. This means mother can go home the same day. Or procedure may be conducted as part of a hospital stay. Procedures may differ depending on condition and healthcare provider’s practices.

Generally, a CVS procedure follows this process:

Mother will be asked to undress entirely, or from the waist down, and put on a hospital gown.
Mother will be asked to lie down on an exam table.
Mother’s blood pressure, heart rate, and breathing rate (vital signs) will be assessed.
An ultrasound will be done to examine the baby’s heart rate and the placenta’s position, baby, and umbilical cord.

Based on the placenta's location, the CVS procedure will be performed through cervix (transcervical). Or it will be done through abdominal wall (transabdominal).

For a transcervical CVS procedure:

The healthcare provider will insert a tool known aa a speculum into vagina so that they can observe mother’s cervix.
Mother’s vagina and cervix will be cleansed with an antiseptic solution.
Using ultrasound guidance, a thin tube will be directed through the cervix to reach the chorionic villi.
Cells will be suctioned through the tube into a syringe. Mother may feel a twinge or slight cramping. More than 1 sample may be required to extract sufficient tissue for testing.
The tube will then be removed.

For a transabdominal CVS procedure:

For an abdominal CVS, mother’s belly will be cleansed with an antiseptic. Mother will be instructed not to touch the sterile area on belly during the procedure.
The medical professional may inject a local anaesthetic to numb the skin.
If a local anaesthetic is used, the mother may experience a sensation of needle prick when the anaesthetic is administered, which could cause a brief stinging sensation.
Ultrasound will be utilised to aid guide a long, thin, hollow needle through belly and into the womb and placenta. This may be slightly painful. The mother may feel a cramp as the needle enters the womb.
Cells will be delicately drawn into a syringe using gentle suction. Multiple samples may be necessary to obtain sufficient tissue for testing.
The needle will then be taken out. An adhesive bandage will be kept over the abdominal needle insertion site.

What happens after chorionic villus sampling?

Mother and baby will be observed for a while during the procedure. The mother’s vital signs and the baby’s heart rate will be assessed periodically for 60 minutes or longer.

The CVS tissue for analysis will be sent to a genetics lab. Counselling with a genetics specialist may be suggested based on the test results.

The mother may have slight cramping and light spotting for a few hours post-CVS.

Mother should rest at home. Don’t do any vigorous activities for at least 24 hours. Don't douche or have intercourse for 14 days or until directed by a healthcare provider.

Mother should call the healthcare provider if she has:

Any bleeding or amniotic fluid leakage from the needle puncture area or the vagina
Fever or shivering
Severe belly pain or cramping

In a nutshell, Chorionic villus sampling (CVS) is a prenatal procedure used to detect chromosomal abnormalities and genetic disorders in the fetus. It involves extracting a tissue sample from the placenta containing genetic material similar to the baby's. CVS procedure is typically performed between the 10th and 12th weeks of pregnancy and may be recommended for women with certain risk factors, like advanced maternal age or a family history of genetic conditions.

Overall, CVS can offer valuable information about the health of the foetus, permitting parents to make informed decisions related to their pregnancy and prepare for any potential challenges that may arise. However, it's important to weigh the procedure's benefits against the potent risks and discuss any issues with a healthcare provider.

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