What Is Chorionic Villus Sampling?
Chorionic villus sampling (CVS) is a prenatal test performed by collecting a sample of chorionic villus cells from the placenta to determine if an unborn child is at risk for chromosomal defects.
Tiny finger-like projections on the placenta called the chorionic villi are taken and sent to the lab for genetic analysis. The placenta provides oxygen and nutrients to the growing baby during pregnancy 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.
The sample is taken through the abdominal wall (transabdominal). Chorionic villi can be analyzed to identify genetic and chromosomal abnormalities. Because the chorionic villi are of fetal origin, examining them can give a clear picture of the genetic makeup of the developing fetus, including Down syndrome (or trisomy 21), Patau syndrome (trisomy 13), Edward’s syndrome (trisomy 18), triploidy and other genetic disorders. CVS cannot, however, test for neural tube and other anatomical defects.
The test produces a karyotype – a picture of the baby’s chromosomes – which provides detailed information on any abnormality.
Women who choose to have CVS are often at increased risk for genetic and chromosomal problems. In addition, the test is invasive and carries a small chance of miscarriage.
CVS is usually done between weeks 11 and 13 of pregnancy — earlier than other prenatal diagnostic tests, such as amniocentesis (where the patient has to be at least 16 weeks pregnant).
Best Choronic Villus Sampling in Chennai
Chennai Women’s Clinic at T.Nagar is one of the best places for Chronic villus sampling in Chennai. We aim to provide all your pregnancy-related tests at top-notch quality and accuracy. Your test procedures are handled under the guidance of an award-winning Obstetrician and Gynecologist in the city, Dr Deepthi Jammi (Founder & Fetal Medical Consultant, Chennai Women’s Clinic).
When Is It Considered?
CVS is offered only if there’s a high risk that the baby could have a genetic or chromosomal condition.
This could be because:
It’s important to remember that the patient does not have to have CVS just because it’s recommended. It’s up to the patient to decide whether she wants it based on the information/counselling provided by the Fetal Medicine specialist.
The test can detect more than 200 different genetic and biochemical conditions. Performing the test early on during the pregnancy gives parents the information they need to cope with some of the complications of the pregnancy or the possibility of terminating the pregnancy.
How Is The Procedure Performed?
The main goal of CVS is to obtain a tiny tissue sample from the placenta, which will be sent to a lab for analysis. The sample will be extracted through the abdomen(transabdominal).
An ultrasound device will be moved over the abdomen and give off / pick up sound waves. The sound waves are used to take a picture of the uterus, the baby, and the placenta on a screen.
These ultrasound waves will be used to help the doctor guide the needle through the abdominal wall and uterus to the placenta. The needle is used to collect a sample of the chorionic villus cells.
Before the procedure, the patient will have an ultrasound to confirm how far along the pregnancy is and make sure it’s possible to get a good sample for the test.
The amniotic sac where the baby is growing won’t be disturbed during the procedure. The procedure takes about 20 to 30 minutes from start to finish, and the extraction itself takes only a few minutes.
However, some patients may experience some pain or discomfort in the abdominal area.
Once the procedure is done, the doctor checks the baby’s heart rate, the patient’s BP along with breathing.
What Kind Of Problems Does CVS Diagnose?
Nearly all chromosomal abnormalities, including Down syndrome, Trisomy 13, Trisomy 18, and sex chromosome abnormalities (such as Turner syndrome). The test can diagnose these conditions, but it can’t measure their severity.
Several hundred genetic disorders. The test is not used to look for all of them, but if the baby is at increased risk for any particular genetic condition, CVS can usually tell whether the baby has the disease.
It should be noted that in the case of CVS, there’s a 1 to 2 percent chance of getting an unclear result. This is called confined placental mosaicism, in which some of the cell lines cultured from the placenta
contain abnormal chromosomes, and some are normal. If the CVS detects mosaicism, the patient will have to get amniocentesis and possibly another test to determine whether the baby is affected.
Factors To Consider When Deciding Between CVS And Amniocentesis?
Both tests can tell whether the baby has a chromosomal problem or certain genetic disorders. CVS is done earlier in pregnancy (usually between 11 and 13 weeks), so the doctor can find out sooner about the baby’s condition.
If there is a severe problem and the patient opts to terminate the pregnancy, she’ll be able to do so while still in the first trimester.
On the other hand, the patient may prefer to wait for the results from second-trimester screening before subjecting herself to an invasive test. At that point, amniocentesis would be the only option.
What Happens After The Procedure?
It is normal to have mild cramping and vaginal spotting and to leak a little amniotic fluid for the first day or two after the procedure.
When Is CVS Not Recommended?
When the patient has an active infection When the patient has experienced vaginal bleeding during pregnancy
What Kind Of Problems Does CVS Diagnose?
What Factors Would Put The Patient At Higher Risk Of Having A Baby With A Genetic Abnormality Or Disorder?
What Are The Risks Of CVS?
- Bleeding and cramping– The patient may experience cramping or bleeding. CVS may cause cramping, leakage of amniotic fluid, and vaginal spotting. These will go away in 1 to 2 days.
- Infection – As with any invasive procedure, there is a risk of infection, though this complication occurs rarely.
- Rh sensitization – During the procedure, there’s a chance that the baby’s blood may be mixed with the mother’s blood. If the patient has Rh-negative blood and the father has Rh-positive blood, the baby has Rh-positive blood, the patient’s body could produce antibodies that attack the baby’s blood cells. If this occurs, the doctor can prescribe Rh immune globulin. This medication will stop the patient from becoming sensitized. If the patient is Rh-negative, the doctor must be informed.
- Accidental abortion or miscarriage – it’s estimated to be between one in 100 and one in 200
CVS also increases the risk of Infection in the uterus. The patient is advised to call the doctor in case of,
The patient should discuss the risks and benefits of the test with the obstetrician. Even though the doctor may recommend the test, the decision to undergo the procedure is entirely up to the patient and her family.
Key Points To Be Noted
- There is a very small chance that CVS could cause bleeding, letting the patient’s blood mix with the baby’s blood. If the patient has Rh-negative blood, she will be given the Rh immunoglobulin vaccine. This can prevent Rh sensitization, which could harm the baby if he or she has Rh-positive blood.
- If CVS finds that the baby has a problem, it is best to talk with the obstetrician and a genetic counsellor. They can help the patient understand the health problem and what to expect when the baby is born.
- The chorionic villus cells may have abnormal genetic material in rare cases even though the baby’s cells are normal. This is called a false-positive result. An abnormal test result may need to be confirmed by amniocentesis.
Frequently Asked Questions
CVS has an accuracy rate of 98%. However, there are 1 to 2% chances of getting an unclear report. This is called confined placental mosaicism. Under this situation, the situation is confirmed with further testing.
These two tests help screen the fetus for some genetic disorders, mainly Down’s syndrome. In amniocentesis, a sample of amniotic fluid is removed from your uterus for testing, while CVS removes a small sample of placenta tissue from the uterus. CVS is effective while screening for genetic disorders, while amnio might be the best option if your partner or your previous baby had a neural tube defect.
Chronic villus sampling gives a very accurate screening of genetic abnormalities and maybe the best option if you want to know to have genetic screening done in your first trimester.
The additional risk of miscarriage is slightly more in CVS when compared with amniocentesis. Please be informed that a CVS or amniocentesis performed by a certified Obstetrician is just around 1%.
NIPT is estimated to have a low false-positive rate of 1 in 1,000. However, if your advised to terminate the pregnancy after your NIPT results, it’s recommended to have a CVS or amniocentesis test performed to confirm the diagnosis.