Chorionic Villus Sampling (CVS)
Chorionic Villus Sampling
Parents are naturally concerned about the health of their unborn baby (fetus). Although most women give birth to healthy babies, certain women have an increased chance of giving birth to a baby with a birth defect. Doctors rely on personal and family medical histories, physical exams, and various procedures and tests to help identify women who may have a baby with birth defects. Some of these women can benefit from Chorionic Villus Sampling (CVS). CVS is a medical procedure performed between 10 - 13 weeks gestation in which tiny pieces of the early placenta (a tissue on the outside of the fetal gestational sac) are obtained for chromosome analysis.
WHO SHOULD CONSIDER CVS?
You and your doctor can decide whether you will benefit from the information provided by CVS. Each woman*s case is different. CVS may be recommended for:
- Women who will be 35 or older at delivery or planning to become pregnant
- Couples who have had a baby with a birth defect
- Couples who have a relative with a chromosome abnormality (e.g. Down syndrome), mental retardation, or other birth defects or medical history of a genetic disorder.
- Couples who have experienced two or more pregnancy losses (spontaneous abortions, stillbirths, or neonatal deaths).
- Couples with an increased risk of having a baby affected with Down syndrome based on first trimester prenatal screening.
- Couples who are concerned about having an abnormal baby.
WHAT IS A CHROMOSOME ABNORMALITY?
Chromosomes are units of genetic information. Babies with a chromosome abnormality usually have mild to severe mental retardation and birth defects. The most common chromosome abnormality is Down syndrome. A chromosome test is performed on cells from the placental tissue (chorionic villi) to determine if the fetus has a chromosome abnormality. The test can also reveal the chromosomal sex of the fetus.
Chromosome abnormalities are caused at conception when an abnormal sperm or egg from one parent fuses with a normal sperm or egg from the other parent. The abnormal sperm or egg contains extra or missing chromosome material. These abnormal sperm or eggs appear to be present in everyone, but the risk of an abnormal conception increases significantly with the parents' ages.
WHICH TESTS CAN BE PERFORMED BY CVS?
Specific tests are performed depending on the indications.
Chromosome analysis - In the laboratory, the cells from the CVS procedure are grown in a special nutritional fluid. Chromosomes obtained from the cells of the fetus are then analyzed. This prenatal test accurately detects about 99% of chromosome abnormalities.
Inherited genetic disorders - Some couples are carriers of genetic disorders which can be detected by CVS. Examples of these disorders for which carrier testing and prenatal diagnosis are available include Tay-Sachs, which is most frequent in the Jewish and French Canadian populations; Sickle Cell, which is most commonly found in African-Americans and Latinos; and Cystic Fibrosis, which is most prevalent in Caucasians of Northern European descent.
Normal results from these tests do not eliminate the possibility your baby may have birth defects and/or mental retardation not detectable by these tests.
To screen for open spine and skull defects which cannot detected by CVS, a maternal serum alpha-fetoprotein (MSAFP) blood test and/or an ultrasound exam are performed at 14 - 16 weeks gestation. These tests detect most, but not all pregnancies with open spine and skull defect.
WHEN CAN CVS BE PERFORMED?
CVS can be performed between 10 - 13 weeks. You and your physician may determine the best timing for your testing.
HOW IS CVS PERFORMED?
If you choose to have CVS, a physician will examine your fetus by ultrasound. A small instrument is gently moved across your abdomen to produce images of the fetus on a TV screen. The ultrasound exam confirms the dating of your pregnancy, and determines the best area for sampling. Some women say CVS does not hurt at all, others feel some pressure or cramping.
Your doctor performs the CVS by placing a small catheter tube through the vagina or abdomen under ultrasound guidance and a small sample of tissue from the placenta is collected. Please do not empty your bladder during the hour before the ultrasound exam. You need a full bladder for this exam. Drink only regular amounts of fluid (without caffeine). For a few women CVS cannot be performed.
IS CVS SAFE?
CVS has been proven to be a safe procedure for both mother and baby. However, spontaneous abortions can occur following CVS, either related to or independent of the procedure. The estimated risk of a spontaneous abortion related to the CVS procedure is about 1% (1 in 100 chances). Recent studies have shown limb reduction birth defects occur in less than 1 in 1000 pregnancies when CVS was performed after 9 weeks of pregnancy, which is not an increased risk. Bleeding, cramping, leaking fluid from the vagina and infection may occur with CVS. Follow your doctor's advice regarding activities to be avoided after CVS. If enough villi are not obtained, a repeat CVS may be suggested. About 1-2% of women receive inconclusive test results which require an amniocentesis.
HOW ARE THE TESTS RESULTS REPORTED?
The chromosome results are usually completed in less than 10 days. Some special genetic testing may require additional time for completion.
Please inform your physician or counselor how to reach you during the two weeks following CVS so your test results can be quickly reported.
Most couples are reassured by these tests because most tests will be normal. If the test results show your baby has a disorder, the nature of the disorder will be discussed with you. Prenatal diagnosis allows couples to make informed decisions and helps with the management of their pregnancy. Supportive counseling is available.
Please discuss any questions you may have with your physician or counselor.
Information provided on this site is for information purposes ONLY. This should not be used as a substitute for professional medical advice, treatment or diagnosis.