Chorionic Villus Sampling (CVS) is a prenatal test that is performed to determine if your unborn child has any genetic defects like Tay Sachs or chromosomal abnormalities such as Down syndrome.
What is a CVS?
During CVS, a sample of the chorionic villus cells is taken for a biopsy. Chorionic villi are tiny finger-shaped growths found in the placenta. Since the genetic material in chorionic villus cells is the same as that in the baby's cells, a genetic analysis can help determine if there are any problems. The procedure is generally done late in the first trimester, most often between the 10th and 12th weeks.
How is a CVS done?
Before you have CVS, you'll have an ultrasound to confirm how far along you are and to make sure it's possible to get a good sample for the test. You may be asked to drink a glass of fluid about an hour before this test so that your bladder is full. A full bladder makes it easier to do the test.
The chorionic villus sample can be collected in two ways: transcervical or transabdominal.
- Transcervical: Here a thin flexible tube (catheter) is inserted through the vagina and cervix into the placenta. Your vagina and cervix are first cleaned with an antiseptic to prevent any bacteria from entering the uterus, which could cause an infection. A gentle suction is then used to get a sample from the placenta.
- Transabdominal: Here a thin, long needle is put through the belly into the placenta. The doctor first numbs a spot on your abdomen with a local anesthetic. If you have a vaginal infection (such as a vaginal yeast infection or genital herpes), a belly procedure will be used instead of a vaginal procedure.
An ultrasound is used to guide the catheter or needle into the correct spot for collecting the sample.
If your blood is Rh-negative, you will need a shot of Rh immunoglobulin after CVS (unless your baby's father is Rh-negative as well) because your baby's blood may have mixed with yours during the procedure and it may not be compatible.
Since this is an invasive prenatal test there is a small risk of a miscarriage. It is important to know that there is a one percent chance of getting a result called a confined placental mosaicism. Here some of the cell lines cultured from the placenta contain abnormal chromosomes and some are normal. If this happens you will be asked to have amniocentesis and possibly other prenatal genetic testing to determine whether your baby is affected.
What does a CVS detect?
- Nearly all chromosomal abnormalities, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). While the test is more than 99 percent accurate in identifying the above conditions it cannot measure their severity.
- Several hundred genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. Although CVS is not used to look for all of them if your baby is at increased risk for one or more of these disorders, the test can usually tell whether he/she has the disease.
- CVS cannot detect neural tube defect such as Spina bifida. You will be offered a blood screening test in your second trimester to determine whether you are at increased risk for these.
When is a CVS recommended?
Your healthcare provider may recommend having this test done if:
- You or your partner has a family history of genetic defects
- You are above the age of 35
- A previous screening identifies you as having a higher than average risk such as:
- A first trimester screening or nuchal fold scan that indicated your baby is at a higher risk for Down Syndrome or another chromosomal problem.
- An early ultrasound showed that your baby has structural defects associated with a chromosomal problem.
- You and your spouse are both carriers of a recessive genetic disorder such as cystic fibrosis or sickle cell disease.
- You have a child with a genetic abnormality and may be at a higher risk of this happening again.
A CVS helps determine your risks and prepare for the future. Specialized prenatal care is the first step towards positive results. Whether or not you have the test done is entirely up to you. Genetic counseling is typically provided to help you understand your prenatal testing options. Having an experienced healthcare technician to perform the test helps reduce the risks associated with the procedure.
Dr. Jorge L. Gomez earned his Medical Degree in 1990 at Central Del Caribe University in Bayamon, Puerto Rico. Following residency in Obstetrics and Gynecology at Bronx-Lebanon Hospital center in the Bronx, NY (1990–1994), he completed additional fellowship training at New York University Medical Center NY, specializing in Maternal Fetal Medicine (1994-1996). After his fellowship in 1996 he joined South Florida Perinatal Medicine. Dr. Gomez is Board certified in OBGYN and Maternal Fetal Medicine. From 2003–2007 He was a reviewer for the American Journal Of Obstetrics and Gynecology.