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Chorionic Villus Sampling (CVS) is a prenatal screening test performed in the first trimester between 10 and 12 weeks of pregnancy. CVS is done to detect specific abnormalities in an unborn baby. A sample of cells is taken from the placenta and tested for genetic defects in Chorionic Villus Sampling test.
Pregnancy is one of the delicate phases in a woman's life which need to be dealt with care. To make sure that the pregnancy tenure of the woman sails smoothly, it is important to make wise decisions and take proper care of the health of the pregnant woman and baby. A set of procedures performed on expectant mothers during pregnancy are called 'Prenatal Screening Tests'. It is useful in determining whether a baby is likely to have specific birth defects during the pregnancy itself. Most of these medical tests are noninvasive and does not have any harm to the mother's and baby's body. These medical tests are usually performed during the first and second trimesters of the concerned pregnancy. Although some are also performed during the third trimester of pregnancy. In this article, we will look at some screening tests including Chorionic Villus Sampling (CVS) test and Amniocentesis test along with the usage of both of these medical tests. (1)
Such screening tests can only provide probability or risks that a particular condition exists. If the results are positive, diagnostic tests can provide a definitive answer.
In this article, we will look at the following aspects:
- What is a prenatal screening test?
- What is the Chorionic Villus Sampling (CVS) test?
- What are the reasons to go for Chorionic Villus Sampling test?
- When is Chorionic Villus Sampling not recommended?
- What are the risks associated with Chorionic Villus Sampling test?
- What is the procedure of Chorionic Villus Sampling?
- What does the result of Chorionic Villus Sampling reveal?
- What is the cost of Chorionic Villus Sampling?
Women who have a higher risk of having a child with certain conditions are usually offered additional screening tests. For example, pregnant women from regions where tuberculosis is common should go for a tuberculin skin test. If the medical practitioner recommends prenatal testing, women should ask how this test is helpful and other questions as well:
- How is this test helpful for patients?
- What will the results reveal and what will they not show?
- What happens if they don't get this test?
- What will they do with their results?
- How précised and are these tests?
- What are the risks associated with these tests?
- How much time is required for these tests to be conducted?
- What does it feel like to undergo these tests?
- What will the results mean for the concerned person and their family?
- Can they decide not to get the results even if the test has been conducted?
- Where should they go for these tests?
Screening tests in the first trimester can begin as early as 10 weeks. These tests usually involve blood tests and an ultrasound. These tests not only help in observing for the baby’s overall development and check to see if the baby is at risk for genetic conditions, such as Down syndrome. They also check the baby for heart defects, cystic fibrosis, and other developmental problems which occurs in the baby during pregnancy.
Screening tests in the second trimester are performed between 14 and 18 weeks of pregnancy. They involve blood test and ultrasound which test whether a mother is at risk for having a child with Down syndrome or neural tube defects.
Chorionic Villus Sampling (CVS) is an important prenatal test where a sample of tissue from the placenta is removed by the medical expert to test it. This test is done to check the chromosomal abnormalities and certain other genetic problems. The sample for the medical test can be taken through the cervix or the abdominal wall of the patient. (2)
The placenta is a structure in the uterus that provides oxygen and nutrients for the growth of the baby. It also removes waste products from the baby's blood during pregnancy. The chorionic villi are one of the important parts of the female reproductive system which come out from the chorion. This chorion is formed from mesoderm tissue present in the mother. The trophoblast cells also contribute to the deriving of chorionic villi. So, they share the baby's genetic makeup. The test cannot be performed before 10 weeks of pregnancy. Chorionic villus sampling helps to understand whether a baby has a chromosomal condition, such as Down syndrome or other genetic conditions like cystic fibrosis. Although chorionic villus sampling provides valuable information about the baby's health, it's important to understand the risks and be prepared for the procedure and results as well.
Chorionic Villus Sampling (CVS) is performed to get information about the baby's genetic makeup. Chorionic villus sampling is usually recommended when the test results show a major impact on the management of the pregnancy or the desire to continue the pregnancy. Chorionic villus sampling is not performed before 10 weeks of pregnancy and earlier than other prenatal diagnostic tests, such as amniocentesis. (3)
One might think about chorionic villus sampling if:
- They had positive results from a prenatal screening test: If the medical test results of a screening test such as the first-trimester screen or prenatal cell-free DNA screening are positive or worrisome, one might opt for chorionic villus sampling to confirm or rule out a diagnosis.
- A woman had a chromosomal condition in a previous pregnancy: If a woman has experienced Down syndrome in a previous pregnancy or the baby was diagnosed with another chromosomal condition. Then this pregnancy might be at a slightly higher risk of being diagnosed with a genetic disorder.
- At the age of 35 or older: If a woman more than 35 years old become a mother then babies born to them have a higher risk of chromosomal conditions, such as Down syndrome.
- History of some Genetic Condition: If someone has a family history of an explicit genetic condition, or they or their partner is a carrier of a genetic condition, then there is a higher risk of a possible diagnosis of a genetic disorder in the baby. Chorionic villus sampling not only identifies Down’s syndrome but can also be used to diagnose many other genetic conditions including single gene disorders such as Cystic Fibrosis and Tay-Sachs Disease.
Chorionic Villus Sampling (CVS) is not helpful in detecting certain birth defects, such as neural tube defects. In the case of neural tube defects, an ultrasound or genetic amniocentesis is recommended by the experts.
The doctor might caution patients against transcervical chorionic villus sampling which is done through the vagina if someone has:
- Vaginal or cervical infection, such as herpes
- Vaginal bleeding or spotting in the previous two weeks
- An inaccessible placenta, due to a tilted uterus or noncancerous growths in the cervix or the lower part of the uterus in a woman
- Have an active infection of Sexually Transmitted Diseases (STD)
- If a woman is carrying twins in a pregnancy
- Have experienced vaginal bleeding during pregnancy
- Diagnosed with uterine fibroid
Rarely, the medical expert will recommend not to go for transabdominal chorionic villus sampling (Transabdominal CVS) which is done by the abdominal wall if:
- The uterus is tilted backward and placenta is located at the back of the uterus. (4)
Every medical test has some specific risks which need to be dealt in a smart way under the expertise of the trained medical doctors. CVS test has the following risks associated with it:
- Miscarriage: The chances of miscarriage after going through chorionic villus sampling is probable to be 0.22 percent. This explains that 1 in every 100 women might face miscarriage after having a CVS test. However, it is not confirmed that which miscarriages would have happened anyway, and which are due to CVS test. As per some recent researches, only a very small number of miscarriages occur after the CVS test is completed are a direct result of this test. If miscarriages happen after Chorionic villus sampling test then they occur within 3 days of the procedure. There is no evidence to suggest what one can do during this time to reduce the risk of miscarriage. (5)
- Rh sensitization: Chorionic villus sampling might cause some of the baby's blood cells to enter the bloodstream. If someone has Rh-negative blood and has not developed antibodies to Rh-positive blood, they will be given an injection of a blood product called Rh immune globulin after chorionic villus sampling. This will prevent their body from producing Rh antibodies that can cross the placenta and damage the baby's red blood cells. A blood test can detect if someone has begun to produce antibodies.
- Infection. There are very rare chances of infection by chorionic villus sampling. It might trigger a uterine infection.
As per some old research papers, chorionic villus sampling might cause defects in a baby's fingers or toes. However, this risk only arises if the procedure is done before week 10 of pregnancy. One should contact their healthcare provider if these symptoms remain or get worse. (6)
It is also advisable to contact the doctor if someone experiences:
- Leaking of amniotic fluid
Preparation for Chorionic Villus Sampling Test:
One might need to have a full bladder for chorionic villus sampling. It is advisable to check with the healthcare provider about how much fluid one might need to drink, and any other pre-test preparation that might be necessary before the test procedure appointment.
The health care provider will explain the procedure and ask the concerned person to sign a consent form before the procedure begins. It is better to visit the clinic with someone for emotional support and have help who can drive home afterward.
What to Expect from the CVS test?
CVS test is an indicative medical test that detects chromosome abnormalities and genetic disorders with high levels of precision which ranges up to 99%. The probabilities of detection are high for this test, but it does not measure the severity of these specific disorders. This medical test does not help to discover neural tube defects. Chorionic villus sampling is performed at the health care provider's office under the expertise of a trained and experienced medical specialist.
First, the health care provider uses ultrasound to verify the baby's gestational age and the position of the placenta in the womb. The patient lies on their back on an examination table with their abdomen exposed. The doctor applies a special gel to their abdomen, and then use a small device known as an "ultrasound transducer". This medical device is used to show the baby's position on a monitor. Next, the doctor uses the ultrasound image as a guide and take a tissue sample from the placenta while the patient keeps lying still. This can be done through the cervix or abdominal wall of the concerned patient. (7)
- Transabdominal chorionic villus sampling: After cleansing the abdomen with an antiseptic, the doctor inserts a long, thin needle through the abdominal wall and into the uterus. One might notice a stinging sensation when the needle enters the skin. One might feel cramping when the needle enters the uterus. The tissue sample from the placenta withdraws into a syringe, and the needle is removed.
- Transcervical chorionic villus sampling: After cleansing the vagina and cervix with an antiseptic, the health care provider opens the vagina with a speculum and inserts a thin, hollow tube through the cervix. When the catheter reaches the placenta, gentle suction is used to remove a small tissue sample.
After the CVS procedure:
One might experience a small amount of vaginal bleeding immediately after the procedure. One can resume their normal activity level after the procedure. However, it is better to consider avoiding strenuous exercise and sexual activity for a day.
Meanwhile, the tissue sample is analyzed in a lab. It may take a few days to a week or so for the declaration of results. It depends on the intricacy of the lab analysis.
Contact the health care provider in case of:
- Fluid leaking from the vagina
- Heavy bleeding
- A Fever
- Uterine contractions
The health care provider or a genetic counselor helps the concerned person understand their Chorionic Villus Sampling (CVS) results. Most of the times, medical test results are unclear and amniocentesis is required. Amniocentesis is another prenatal diagnostic test which is needed to clarify the diagnosis.
There's a rare chance of a false-positive test with chorionic villus sampling when the test is positive, but in reality, no disease exists in the baby. It's also a noticeable point that chorionic villus sampling is not able to identify all birth defects, including spina bifida and other neural tube defects. (8)
If chorionic villus sampling indicates that the baby has a chromosomal or genetic condition that can't be treated, the patients face wrenching decisions. It becomes a hard choice to decide whether to continue the pregnancy or not. During such tough times, one should look for support from their health care team and loved ones.
Uncertain results are more likely to occur with CVS when compared to the results achieved with amniocentesis. The reason for this is that the CVS procedure is more likely to be contaminated with cells from the mother, occasionally making them difficult to distinguish from the baby. Also, occasionally the 'cultured' or 'grown' cells develop subtle changes from the original cells. This makes the chromosomes have a slightly different configuration and appearance, artificially creating different cells called 'pseudo-mosaics'. It is impossible to interpret these cells, making the results of the CVS inconclusive for the respective case. This would mean repeating the CVS test or having an amniocentesis test once the doctor suggests the right time for it.
Injuring the Baby:
When a CVS is done very early during the concerned pregnancy (less than 9 weeks of pregnancy) there is a greater chance (up to 2% or 1:50) that the baby will develop limb or facial abnormalities. It is technically possible to perform a CVS test as early as 6 to 8 weeks of pregnancy, but it is not usually recommended until after 10 weeks of the same pregnancy. CVS test done too early can cause hemorrhage effect on the baby's limbs and face, possibly leading to the baby losing fingers, toes, or part of their legs or arms. The medical term for this condition is 'limb reduction'. The possibility of this happening with a CVS test done after 10 weeks of pregnancy is quite rare, about 1: 2000 (or 0.05%).
Some caregivers do consider very early CVS in some circumstances. For example, according to Orthodox Jewish law termination of a pregnancy (or abortion) is only permitted before 40 days after the conception of the baby (or 8 weeks of pregnancy). Therefore, an early CVS test may be offered to women who feel strongly about performing the test early, being made fully aware of the increased likelihood of the baby being injured or miscarried during the pregnancy.
Haemangiomas (also known as strawberry marks) are like birthmarks that are usually caused by an overgrowth of tiny blood vessels called 'capillaries' underneath the baby's skin. These create bright red (or purplish), soft, raised, spongy swellings which have a resemblance to a birthmark. Haemangiomas were more common in babies whose mother underwent CVS test during pregnancy (1.3%) when compared with early amniocentesis. (0.1%). (9)
CVS procedure cost depends on where one gets it. The role of the hospital is very important in determining the cost of a medical test or procedure. It also gets affected by whether someone has insurance or not. Many insurance plans cover at least some of the cost of CVS, but it should be checked before the treatment with the insurance company to be sure. If someone does not have insurance or their plan does not cover the procedure. Then they will have to pay for it themselves. They can get more in-depth information from their doctor’s office about Chorionic Villus Sampling (CVS) costs and available payment plans. (10)
Alternative of Chorionic Villus Sampling (CVS):
An alternative of CVS test is Amniocentesis test. In the Amniocentesis test, a small sample of amniotic fluid is removed for testing. This fluid surrounds the baby in the womb.
This medical test is usually performed between the 15th and 18th week of pregnancy. It can also be performed later, if necessary. Amniocentesis test has a similar risk of causing a miscarriage, but the pregnancy will be at a more advanced stage before one receives the test results. So, the concerned person has less time to consider the options available for them. (11)
CVS vs Amniocentesis:
During pregnancy making a decision about diagnostic tests such as CVS or amniocentesis can be difficult for a couple. One needs to make this decision alone or with their partner. It may be helpful to talk through all the options with the doctor or midwife before finalizing a particular medical test. One should discuss all the options with a pediatrician and consultant geneticist or genetic nurse counselor before opting for the procedure. One may also want to know more about what is involved in ending a pregnancy and how they may feel afterward. (12) The obstetrician or midwife should discuss the following information with the concerned person:
- The disorders that can be detected by amniocentesis or CVS
- Which test would be recommended in their situation
- The types of laboratory tests available and what the results will tell the concerned person
- The reliability of the laboratory test
- Risk of having an uncertain result
- The risk of miscarriage from CVS or amniocentesis including the risk in their own unit at this time
- How long the results take
- How the results will be revealed
- What are the options if the baby is found to have a genetic disorder
Difference between CVS and Amniocentesis:
In making a decision about having a diagnostic test such as CVS or amniocentesis, it is important that one has enough time and that they feel supported in the final decision. The concerned person should be given time to discuss their doubts related to the medical test and be able to request any further information. The final decision is taken after consulting the concerned doctor. (13)
Name of the Test
How is it taken?
A small sample of the placenta under ultrasound guidance is taken
Sample of amniotic fluid that surrounds the baby in the uterus is taken under ultrasound guidance
Time of the procedure
Between 10 -14 weeks of pregnancy
After 15 weeks of pregnancy
Risk of miscarriage
About 1 to 2 in 100 women (1-2%) may face miscarriage following the procedure
About 1 in 100 women (1%) may face miscarriage following the procedure
What is involved in ending the pregnancy?
At this stage, it may involve a small operation to empty the womb or tablets to bring an on miscarriage
When a pregnancy is ended later it involves going into labor
If someone is offered tests to look for a genetic or chromosomal condition in the baby, a specialist involved in carrying out the test discusses the different options with the concerned person. It helps them make the right decision.
Frequently Asked Questions (FAQs):
- Is amniocentesis painful?
Some of the women have given an opinion that amniocentesis gives a similar amount of discomfort which occurs in a regular blood test. One will not usually need a local anesthetic during this medical test.
- Can someone have a CVS or Amniocentesis if she is pregnant with twins?
Yes, one can have a CVS or Amniocentesis if they are pregnant with twins. It is very important to know that from the respective baby's placenta the sample of placenta or fluid has been taken. If the results show one of the babies has a disorder, the concerned couple needs to know which baby is affected. The medical specialist can be consulted for the required guidance based on the results of the test. CVS or amniocentesis in multiple pregnancies is carried with a high level of expertise in ultrasound scanning by the doctors. This means one needs to be referred to a fetal medical center specialized for genetic counseling. The doctor inserts the needle twice to get samples of the placenta from each baby. In the case of the CVS test, there is a chance of getting two samples from the same baby that gives misleading results. The risk of miscarriage is more in amniocentesis with twins (1 in 56). If this happens it may lead to loss of both babies conceived with the pregnancy. (14)
- Is a Chorionic Villus Sampling (CVS) test painful?
Most women are in the opinion that CVS is uncomfortable rather than painful. Some women reveal that transcervical method is like having a cervical smear taken during the test.
- Is Amniocentesis better than other CVS tests?
Amniocentesis is better than CVS for some women. One should undergo amniocentesis test if they have had a baby with a neural tube defect, such as spina bifida. If the concerned person or their partner has a neural tube defect then also amniocentesis is better. CVS does not test for these problems concerning fetus. Amniocentesis will be considered a better choice if the results of other tests do not come normal. CVS may be better if the concerned person or their doctor wants to know the test results during the first three months of pregnancy.
Hope this article was helpful for you in getting all the information about Chorionic Villus Sampling (CVS). For more such informative articles, you can refer to OVO Fertility blogs. The team at OVO Fertility is constantly striving to make sure that infertile couples are aware of their health status associated with infertility treatments. Thousands of couples have been benefitted by OVO Fertility expert team's advice and suggestions with respect to planning a baby. For any assistance concerning infertility procedures, feel free and talk to the experts on the given number: +918268260808.
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