Chorionic Villi Sampling - Types, Procedure, and Complications

What Is Chorionic Villi Sampling?

Chorionic villus sampling (CVS) is a prenatal diagnostic test done after 11 weeks of pregnancy to diagnose if the baby has any chromosomal abnormalities, such as Down syndrome or other genetic disorders. CVS helps in making crucial decisions about pregnancy. The doctor takes cells from tiny fingerlike projections on the placenta called the chorionic villi, and it is sent to the lab for genetic analysis. The samples can be collected through the abdominal wall or the cervix. Although chorionic villus sampling can provide important information about the baby's health, it is vital to understand its risks and be prepared for the results.

What Are the Types of Chorionic Villi Sampling?

There are two types of CVS procedures:

• Transcervical - In this type, a catheter is inserted into the placenta through the cervix to obtain the tissue sample.

• Transabdominal - In this type, a needle is inserted into the placenta through the abdomen and uterus to obtain the tissue sample.

Why Is Chorionic Villi Sampling Performed?

Chorionic villus sampling may be used for chromosome and genetic testing in the first trimester of pregnancy. CVS procedure is conducted between weeks 11 and 14 of pregnancy, earlier than other diagnostic tests like amniocentesis. Chorionic villus sampling cannot detect certain birth defects like neural tube defects. A genetic amniocentesis or an ultrasound might be recommended if neural tube defects are a concern.

The following are a few reasons that a woman may undergo chorionic villi sampling:

• A family history of a genetic disease, previously affected child, chromosomal abnormalities, or metabolic disorder.

• Maternal age over 35 years.

• Risk of a sex-linked genetic disease.

• Previous ultrasound with questionable or abnormal findings.

• Abnormal cell-free DNA test.

In some instances, the doctors might be cautious against transabdominal chorionic villus sampling if the uterus is tilted backward and the placenta is located at the back of the uterus.

The doctors might be cautious against transcervical chorionic villus sampling if the patient has the following:

• An active vaginal or cervical infection.

• History of vaginal bleeding or spotting.

• An inaccessible placenta because of a tilted uterus or noncancerous growth in the cervix or the lower part of the uterus.

How Is the Chorionic Villi Sampling Performed?

Procedures may vary depending on the condition of the patient and the doctor's practices.

Usually, a chorionic villi sampling procedure follows this process:

• The patient will be asked to lie down on an examination table with the abdomen exposed and place their hands behind their head.

• The vital signs, such as blood pressure, breathing rate, and heart rate, will be checked. Followed by an ultrasound to check the fetal heart rate, gestational age, and the position of the placenta, fetus, and umbilical cord.

• The healthcare providers will apply a gel to the abdomen and then use a device known as an ultrasound transducer to show the baby's position on a monitor.

• Based on the placenta location, the procedure will be performed through the cervix or abdominal wall.

1) Cervical Approach (Transcervical)

The doctor will insert an instrument called a speculum into the vagina, allowing the cervix's visibility. The vagina and cervix will be cleansed with an antiseptic solution. Using ultrasound as s guidance, a thin tube will be passed through the cervix to the chorionic villi. Using a tube, the cells will be gently suctioned into a syringe. The patient may feel a twinge or slight cramping. More than one sample may be collected in some cases to obtain enough tissues for testing. The tube will then be gently removed.

2) Abdominal Approach (Transabdominal)

The abdomen will be cleansed with an antiseptic. A local anesthetic will be injected to numb the skin. This may cause a brief stinging sensation. With ultrasound guidance, a long, thin, hollow needle is inserted through the abdomen into the uterus and placenta. This can cause slight pain and cramps while the needle enters the uterus, and the cells will be suctioned into a syringe. Usually, more than one sample may be collected in some cases to obtain enough tissues for testing. The needle will then be gently removed. A bandage will be placed over the site of the abdominal needle insertion.

How to Prepare for Chorionic Villi Sampling?

Before preparing for the procedure, the following steps are carried out:

• The doctor may ask if the patient is sensitive to or allergic to medications, latex, tape, iodine, and anesthetic agents.

• And the doctor may also ask about the history of a bleeding disorder or if the patient is consuming any anticoagulant or other medications that may affect blood clotting. If so, the doctor may ask to discontinue these medications before the procedure.

• The doctor may check for Rh-negative because, during the CVS procedure, blood cells from the mother and fetus can mix, leading to Rh sensitization and red blood cells breaking down in the fetus.

• Usually, there is no particular diet restriction or activity before the chorionic villus sampling procedure.

• The patient may or may not be asked to have a full bladder right before the procedure because it depends on the position of the placenta and uterus.

• Based upon the medical condition, the doctor may request other specific preparation.

What Are the Risks Associated With Chorionic Villi Sampling?

Some possible complications caused by chorionic villus sampling may include:

• Infection.

• Miscarriage.

• Bleeding.

• Leaking of amniotic fluid (water breaking).

• Preterm labor.

• Limb defects in infants, especially if CVS procedures are done before nine weeks.

• Rh sensitization.

What Factors Increase the Risk of Complications in Chorionic Villi Sampling?

Certain factors or conditions may interfere with the procedure and cause risk to the mother and baby.

These factors include the following:

• Vaginal or cervical infection.

• Amount of amniotic fluid.

• Pregnancy before seven weeks or later than 13 weeks.

• Baby and placenta position.

• Mother's anatomy.

• Samples that are inadequate for testing.

Conclusion:

Chorionic villi sampling is a diagnostic test that provides information about the baby's genetic and chromosomal condition. It has two approaches. Depending on the patient's condition, a suitable method will be selected. It is a simple test with minimal pain; the procedure takes only 30 minutes.