Chorionic villus sampling, commonly known as CVS, is a medical test used to detect chromosome abnormalities and inherited disorders. Your healthcare provider may suggest this test if you or your partner have a family history of certain conditions that could pose risks. One of the main advantages of CVS is that it provides results early in your pregnancy, often giving you peace of mind sooner.
How is CVS Conducted?
CVS involves the extraction of chorionic villi cells from the placenta, where it attaches to the uterine wall. There are two primary methods for obtaining these samples:
- Transcervical Method: Guided by ultrasound, a thin catheter is inserted through the cervix to reach the placenta. The chorionic villi cells are then gently suctioned into the catheter. This is the most common approach.
- Transabdominal Method: In this method, a long, thin needle is guided through the abdomen to the placenta using ultrasound. A sample of tissue is drawn and the needle is then removed. This technique is similar to amniocentesis.
Before performing the CVS, your doctor will utilize ultrasound to determine the best approach to reach the placenta safely. Generally, only one attempt is necessary to obtain a sample, but in the case of twins, separate procedures may be required for each baby. In rare situations, a second attempt might be needed, or it may not be possible to collect enough cells.
The advantage of CVS over amniocentesis is that it collects larger samples and offers quicker results, typically within one to seven days.
Timing for CVS
CVS is generally performed between 10 and 13 weeks of pregnancy. Many choose CVS over amniocentesis to get results earlier. If you’re considering this test, be sure to contact your healthcare provider early in your pregnancy to schedule it.
What Does CVS Test For?
CVS examines the baby’s chromosomes by analyzing placental cells. Since the placenta and the baby share the same genetic information, the lab can grow and study these cells to learn about the baby’s genetic health. Chromosomes are tiny structures that hold our DNA, which contains the instructions for human development. Typically, each cell has 46 chromosomes. CVS can identify if there are extra chromosomes, missing ones, or significant structural changes. Such abnormalities may lead to serious birth defects or developmental issues.
The test can also assess for specific inherited genetic conditions. For instance, if there’s a known risk of conditions like cystic fibrosis, sickle cell disease, or Tay-Sachs disease in your family, CVS can be used to test for those conditions. Down syndrome, caused by an extra 21st chromosome, is the most frequently detected condition. Trisomy 18, or Edward syndrome, is less common but serious, often resulting in significant complications.
It’s important to note that CVS does not screen for all birth defects, such as heart issues or spina bifida. If you’re interested in testing for spina bifida, measuring alpha-fetoprotein in the mother’s blood or an ultrasound around 18 to 20 weeks could be options to consider.
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Test Results
Typically, results from CVS take about 10 to 14 days. If time is of the essence, preliminary results can sometimes be available within 48 hours. However, if the placental cells grow slowly in the lab, results may be delayed. In rare cases, if placental cells do not grow at all, you might need to repeat the CVS.
If the pregnancy has progressed beyond 14 weeks, amniocentesis may be considered instead. Special genetic testing may extend the timeline for results, sometimes taking over a month.
Accuracy of CVS
CVS boasts an accuracy rate of approximately 99 percent for common chromosomal issues. If specialized genetic testing is conducted alongside CVS, the accuracy may vary depending on the specific condition being tested.
In summary, chorionic villus sampling is a valuable tool for early diagnosis of genetic conditions in pregnancy. It provides critical information to expectant parents, allowing for informed decisions regarding their pregnancy and family planning.