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Chorionic villus sampling

Chorionic villus sampling (CVS) is a test performed in some pregnant women to screen their babies for the diagnosis of any birth defects or pregnancy-related issues. Chorionic villus sampling can also help in early diagnosis of any chromosomal disorders e.g. Down’s syndrome or for any genetic problems e.g. cystic fibrosis or sickle cell anemia. In Chorionic villus sampling, a small part of the chorionic villi (a small sample of cells) is taken from the placenta and from there it is attached to the wall of the uterus for the diagnosis and testing. The sample to be used for testing can come from either the abdominal or the cervix wall. At the time of pregnancy, the placenta supplies nutrients and oxygen to the unborn baby and also cleans the baby’s blood by taking out the waste.

Chorionic villi are very small wispy protuberances that form the placenta. They develop from the fertilized eggs and share the genetic makeup of the baby. They have the genes which are very similar to the genes of the baby.

Why it's done? What are the risks? How to prepare for the procedure? Expected Results from the Procedure: FAQ Section:

Chorionic villus sampling is done in order to identify any genetic/birth defects in the unborn. CVS can be done 10 to 12 weeks of pregnancy. It is very accurate and helps to manage the pregnancy in the initial stages. This in turn helps in making the decision that whether a mother desires to terminate the pregnancy (in case of abnormal results) or continue. 

There are multiple factors, which might be usually considered while deciding on whether the Chorionic villus sampling procedure is required to be conducted or not. Some of these factors are as mentioned.

  • Chromosomal issues/defects in the earlier pregnancy- If the earlier pregnancy had some chromosomal defects like Down’s syndrome or any other, then the chances of reoccurrence of these defects can be high in the present scenario as well. In such cases, CVS is usually preferred to assess the condition.
  • Abnormal outcomes of a prenatal screening test- If the results are positive from the screening test in noninvasive prenatal testing or from the first trimester screen test, then CVS can be very helpful to provide an early diagnosis.
  • 35 years of age or above- In the women with 35 years of age or older on the due date there is a very high risk of chromosomal/ birth defects e.g. Down’s syndrome.
  • Spontaneous abortions: If the mother has experienced spontaneous abortions in the past, then CVS can be useful in assessing the present situation
  • Genetic Disorders in parents- If the mother herself or the partner has had any history of genetic disorders, CVS could be useful in understanding if the genetic disorders would be passed on to the child.
  • Family history of genetic disorders- In case, if any family member has a history of any genetic disorders such as Tay- Sachs disease, or Cystic fibrosis, Chorionic villus sampling is very useful to rule out any passage of these problems to the newborn.

Though the procedure is usually very helpful in screening and diagnosis of any defects in the unborn babies, there are some risks associated with the CVS procedure. Some of the risks are as highlighted.

  • Miscarriage – The risk of miscarriage is usually lesser than 1 in 100. The risk is even lesser when the tissue sample is taken from the abdominal wall (transabdominal) as compared to the cervix (trans cervical). However, if the baby is smaller than his/her normal gestational age, the risk of miscarriage increases. Some other abnormalities or situations like the rupturing of the membranes may also lead to increased incidences of miscarriage.
  • Rh sensitization – Sometimes, while conducting the CVS procedure, some of the blood cells of the unborn baby might enter into the mother's bloodstream. This can be prevented in the case if the mother has Rh-negative blood and has not formed antibodies to Rh-positive blood. In such cases she could be administered with a drug called Rh immunoglobulin. This drug will be given after the procedure in order to prevent the formation of antibodies against the blood cells of the unborn (Rh incompatibility).
  • Infection – The pregnant mother might acquire some uterine infections.
  • Bleeding- Mother can experience bleeding and in some cases cramping as well if the procedure was done through cervix.

Some rare cases reported after the procedure included defects in the fingers and toes of the baby especially when the CVS was performed anytime before the ninth week of pregnancy.

Before the procedure:

There are certain steps and guidelines, which a Hospital would follow while preparing for the CVS procedure. Some of the steps undertaken by the Hospital are as mentioned

  • The procedure will be explained in detail to the mother and the family along with its risks.
  • The person undergoing the procedure may be asked to sign a consent form.
  • The person undergoing the procedure would have to usually wear a hospital gown during the course of the procedure.
  • The person undergoing the CVS is asked to drink a lot of water/fluids before the procedure in order to have a full bladder. This makes it easier for the healthcare provider to perform the ultrasound.
  • In case the mother is allergic to shellfish or iodine, she needs to inform the same to the healthcare provider beforehand.
  • It is advised to bring along a companion to take back the pregnant mother safely.

Chorionic villus Sampling is usually performed in the outpatient department. Firstly, an ultrasound will be performed to determine the gestational age of the baby and the exact position of the placenta. This is done usually 10-12 weeks from the women’s previous menstrual cycle so that CVS can be carried out at the suitable gestational age.

During the procedure – When the ultrasound is performed, the woman has to lie on the examination table with the abdomen exposed. A water-based clear gel is applied to the abdomen and the provider will operate with a small device called an ultrasound transducer to show the position of the baby on the screen. This ultrasound image will be further used as a guide to take a small sample from the placenta. This can be approached in 2 different ways and the entire procedure would typically take around 30 minutes of time.

  1. Cervix (Transcervical) – If the position of the placenta is favorable, then the sample can be taken from the cervix. The provider will clean the vagina and cervix with an antiseptic, following which the provider will open the vagina with a speculum and slide a narrow, hollow tube through the cervix. A light suction will be felt the moment the catheter reaches the placenta and a small tissue sample will be removed. The women might feel a slight cramp while the sample is extracted.
  1. Abdominal wall (Transabdominal) – The procedure is performed and the sample is taken through the Abdominal wall if there is any cervical infection like herpes or if the placenta cannot be accessed properly through the cervix. The abdomen is first cleansed with an antiseptic and a very fine and long needle is inserted into the abdomen wall and the uterus. There might be a slight stinging sensation when the needle enters the abdomen wall and a slight cramp when it enters the uterus. The sample is then extracted through a syringe.

After the procedure – After taking the tissue sample, the heart rate of the baby is checked. There might be some bleeding from the vagina immediately after the procedure. The samples are sent to the lab for further analysis. The cells are grown in a special fluid in the lab and the results for the test might be available after 7-10 days.

The mother should inform her healthcare provider in case the following abnormalities are observed.

  • Heavy bleeding
  • Uterine contractions
  • Fluid leaking from the vagina
  • Fever

The healthcare providers can best explain the results from the Chorionic villus Sampling test and they should be consulted immediately after the reports as available.

  1. Normal results – The normal results from the test indicate that there is no genetic defect in the unborn baby.
  2. Unclear Results- In case the results from the test are not very clear then the healthcare provider might ask the mother to go for amniocentesis (another prenatal test).
  3. Abnormal results – If the results from the test are not normal, then a range of abnormalities such as Down’s syndrome, Hemoglobinopathies or Tay- Sachs disease can be identified from the results.
  4. There might be certain cases where the CVS results are positive and there are no signs of any disease, but still the mother might have to go through some additional tests. It is important to note that the CVS procedure cannot identify all the birth defects including spina bifida and other neural tube defects.
  5. In a case the results show that the unborn has any genetic or chromosomal disorder which is not treatable, then the decision can be taken by the couple whether to continue the pregnancy or not.

CVS is one of better procedures to understand the abnormal conditions or disorders related to pregnancy. The results can help to find out about the potential problems, the child might have at the time of or even after the birth. This can in turn allow patients to take preventive measures and treatments beforehand and make an intervention at a very early stage of a disease.

Q1. What are the things that a mother should be careful about and be updating her healthcare provider before undergoing the CVS procedure?

A1. The healthcare provider might ask the pregnant women to be aware of the following points before undergoing CVS- transcervical:

  1. Spotting of blood or bleeding from the vagina in the past two weeks.
  2. Incidence of any cervical blockage or narrowing (cervical stenosis)
  3. Any cervical infection
  4. Involuntary vaginal wall spasms (vaginismus)
  5. Prevalence of uterine fibroids (non -cancerous growth) or tilted uterus

Q2. What are the diseases and disorders which the chorionic villus sampling can identify in unborn babies

A2. CVS is a very useful procedure performed during pregnancy to understand and identify a range of disorders in unborn babies. These disorders include chromosomal disease like Down Syndrome, sex related disorders such as muscular dystrophy in males, or genetic disorders including Tay-Sachs disease, or Cystic Fibrosis.

Q3. Is the CVS test painful and difficult to undertake

A3. The test can be painful in certain cases, however with the range of advanced technology available and with a team of experienced and knowledgeable doctors at Fortis, the test can be conducted without much hassle in less than 30 minutes.



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