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Chorionic villus sampling (CVS) is a prenatal test performed during pregnancy 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. During pregnancy, the placenta provides oxygen and nutrients to the growing baby 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 analysed 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 those at increased risk for genetic and chromosomal problems.The test is invasive and carries a small risk 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).
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 types of 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.
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).Ultrasound will be used to help the doctor guide the needle to the placenta. Gel will be rubbed on the abdomen and a local anaesthetic is administered at the procedure site. An ultrasound device will be moved over the abdomen and will give off / pick up sound waves. The sound waves are used to make a picture of the uterus, the baby, and the placenta on a screen. The doctor can also use ultrasound to check the baby's heart rate. The doctor then puts a long, thin needle through the abdominal wall and uterus to the placenta. The needle is used to collect a sample of the chorionic villus cells.
After the sample is collected, the doctor may listen to the baby's heart beat.
Before the procedure, the patient will have an ultrasound to confirm how far along the pregnancy she is and to make sure it's possible to get a good sample for the test.
During the procedure, the amniotic sac where thebaby is growing won't be disturbed. The procedure takes about 20 to 30 minutes minutes from start to finish and the extraction itself takes only a few minutes. Some patients may experience some pain or discomfort in the abdominal area.
CVS can identify:
Some factors to consider include:
Some of the risks involved with the procedure include:
CVS also increases the risk of Infection in theuterus.
The patient is advised to call the doctor in case of,
The patient should discuss the risks and benefits of the test with theobstetrician. Even though the doctor may recommend the test, the decision to undergo the procedure is entirely up to the patient and her family.
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 serious 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.
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.