Chorionic villus sampling (CVS) is an antenatal test to confirm whether or not your baby has a particular genetic condition such as Down syndrome. CVS can also test for other inherited conditions, including thalassaemia and sickle cell anaemia CVS is offered in pregnancies where there is a high risk of the baby having a serious inherited condition. This could be because: you are over 35 you have had a previous pregnancy where the baby had problems such as a chromosome abnormality or another serious health condition you have a family history of a condition such as cystic fibrosis or muscular dystrophy an antenatal screening test, such as the combined first trimester screening test or the non-invasive prenatal test (NIPT), has suggested that the baby may have a health problem When is CVS carried out? A CVS is usually done between 11 and 13 weeks of pregnancy. In special circumstances, the CVS might be carried out later, but it should not be done before 10 weeks of pregnancy. Types of antenatal tests There are two main types of antenatal tests: screening and diagnostic. CVS is a diagnostic test. It offers more information than screening tests, which are offered to all pregnant women. Screening tests pick up clues that your baby may have a particular condition. If an initial screening test suggests a higher risk, it may be followed by a diagnostic test, like CVS. CVS can tell you for sure whether or not your baby has the condition. One example is a screening test for Down syndrome. This is usually offered in India to older pregnant women who are above the age of 35. However, if your doctor feels that a Down’s syndrome screening test is needed just to be sure, he/she may ask you to take it irrespective of your age. How CVS is performed? During CVS, a sample of cells, called ‘chorionic villi cells’, is taken from your placenta using one of the procedures below: Transabdominal CVS — A needle is inserted through your abdomen, observed at all times by ultrasound. The needle does not enter the amniotic sac or go near the baby. The procedure is performed under local anaesthetic. Transcervical CVS — A tube is inserted through your cervix (the neck of the womb) and observed by ultrasound. You don’t need an anaesthetic — it’s similar to having a pap smear. The test takes about 5 minutes, although the whole consultation will take about 30 minutes. CVS has been described as uncomfortable rather than painful, and there may be some cramps afterwards which are similar to menstrual cramps. Risks of CVS CVS increases your risk of miscarriage, but only 1 in every 100 pregnancies that end in miscarriage would be directly due to CVS. This risk is in addition to the ‘background risk’ of miscarriage that all women have in early pregnancy due to natural causes. It is important to discuss your risk of miscarriage with your doctor, midwife or genetic counsellor. The specific figure for the risk of a miscarriage depends on the experience of the doctor doing the test and the difficulty he or she has in obtaining the sample. It is therefore important that a CVS test is only carried out by a doctor experienced in this technique and it should be done after the 11th week of pregnancy. You may have some vaginal bleeding after a CVS. Talk to your doctor about what you can expect after the testing and what symptoms to look out for. Content source Featured image source
Why and how CVS test is done?
Written by Dr. Himanshu Chaudhary (Gynaecologist)223 Views
The Chorionic Villus Sampling or CVS Test is prescribed between the 10th to 12th weeks of gestation. It is a prenatal test, which helps detect genetic diseases, birth defects, and any other issues related to the pregnancy.
What happens in the CVS Test?
In the CVS test a tiny bit of Chorionic villi is drawn out from the placenta as sample. This sample is taken from the place where the placenta is attached to the uteral wall. The Chorionic Villi are taken because they possess the same genes, which will be present in the baby eventually. Therefore, they make the best sample to ascertain whether the baby is at risk of developing any genetic diseases or birth defects. This test helps detect any such conditions early in the pregnancy.
Diseases and Disorders Easily Identifiable Via The CVS Test Here are some diseases that the CVS test helps detect timely and with 98% accuracy –
- Chromosomal disorders such as - Down syndrome
- Genetic diseases like - cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and sickle cell anemia.
- Gender specific disorders such as - muscular dystrophy commonly seen in male babies. This test is also used to identify the gender of the foetus as well.
Who is suggested the CVS Test?
Experts advise that the CVS test may only be suggested to women who are at a greater risk of having babies with genetic defects and disorders.
These include -
- Couples where one partner already has a genetic disorder or carries a genetic disease/chromosomal abnormality.
- Couples with a family history of birth defects either in a previous pregnancy or a family member who has birth defects.
- A pregnant woman 35 years or older on her due date. Higher the age of the woman, greater is the risk of the offspring having chromosomal defects such as Down syndrome.
- A pregnant woman who displays abnormal results in genetic tests. It is, however, a couple’s choice whether to get the test done or not.
Advantages of the CVS Test
- CVS takes place very early in the pregnancy. It is done even before amniocentesis. Therefore, it informs about defects and diseases quite early allowing timely action and appropriate choices.
- The results of the CVS test come within 10 days.
- Termination of pregnancy upon receipt of abnormal test results is much safer for the woman since the same is done early in the pregnancy.
Disadvantages of the CVS Test
- The CVS poses a little higher threat of miscarriage as compared to amniocentesis, as it is done very early in pregnancy.
- Risk of infection too is higher at this stage.
The CVS Test Procedure Counseling - When someone is recommended a CVS test, she is given elaborate genetic counseling that involves detailed information of the advantages and disadvantage of taking the test. The risks involved are clearly communicated to the patient so that an informed decision can be made.
Ultrasound - After the counseling an ultrasound examination is done to ascertain the gestational age of the foetus and to identify placental location. This is because it is best to perform the CVS test 10 to 12 weeks from the last menstrual period of the woman.
Collection of the chorionic villi - The chorionic villi are collected from the placenta either via the abdomen or the vagina. A quick test, it takes hardly 30 minutes in all. The procedure might be slightly painful to some women. There are two ways of collecting the sample.
These are -
- The abdominal collection - This is done using a needle. This needle is inserted into the placenta through the mother’s abdomen.
- The vaginal collection - This is done using a speculum, which is inserted in the vagina. Then, a small portion of the placenta is removed by inserting a thin tube of plastic into the cervix via the vagina. Ultrasound imaging is used to guide the whole process.
Laboratory sample testing - The collected sample is sent to the lab. Here it is cultured for in a fluid for further testing after a few more days.
Results - The results are made available to the patient in two weeks.
Precaution to take after the CVS Test
- Take it slow and easy once the test is over. Get off the bed slowly and take assistance while you steady yourself.
- Avoid driving yourself back home. Make sure someone assists you to the hospital and back.
- Rest well the rest of the day and preferably put pillows under your feet for added comfort.
- It is normal for doctors to advise abstinence from exercise, strenuous work, and sex for the next three days to avoid any stress.
- Experiencing minimal bleeding and some cramps are normal. However, the same must still be reported to the doctor.
- Any discharge or fluid leaks from the vagina must immediately be reported to the doctor without any delays. The test when suggested is in your best interest. It is therefore advised that if your doctor feels the need for a CVS test, you must consider it to ensure you have a healthy baby.