If you have a family history of genetic problems, or you are over 35 years old, your midwife or OB/GYN will recommend that you undergo a prenatal diagnostic test to identify genetic abnormalities in your baby. Chorionic villus sampling (CVS) and amniocentesis are two common diagnostic tests that your healthcare provider may recommend.
In this article, I will be discussing the risks and benefits of chorionic villus sampling – also known as CVS testing. Some women with a family history of a genetic disorder choose to have chorionic villus sampling, rather an amniocentesis, because it is performed in the first trimester so you will get your results sooner.
What is Chorionic Villus Sampling?
Chorionic villus sampling (CVS) is a prenatal test that has been widely performed worldwide since the 1980s. Like with an amniocentesis, it detects chromosomal and abnormalities and genetic disorders in the developing baby. CVS testing involves a biopsy of the placenta. During the procedure, your doctor will remove a small piece of placental tissue – called chorionic villi, which are tiny fingerlike, wispy projections that have the same genetic make-up as your unborn baby. The chorionic villi will be sent to a lab for analysis, and you can get your results back within a few days or 7 to 10 days, depending on the lab. Ask your doctor for his/her policy.
This prenatal diagnostic procedure is performed late in the first trimester – typically between 10 and 12 weeks of pregnancy, though some testing centers may perform it at 13 weeks pregnant.
Chorionic villus sampling can diagnose nearly all chromosomal abnormalities, including trisomy 13 and trisomy 18, Down syndrome, and sex chromosomal abnormalities (like Klinefelter syndrome and Turner syndrome). CVS testing can also detect several hundred genetic disorders – including sickle cell disease, Tay-Sachs disease, cystic fibrosis and others.
Why Choose CVS Testing?
There are many reasons why a pregnant woman would choose to have CVS testing. Because chorionic villus sampling provides information about the health of her developing baby, it may have an impact on how your doctor manages your pregnancy, and it may also affect your decision on continuing your pregnancy. Some women do not want to have a baby with a genetic defect. On the other hand, if you’re against abortion, having a CVS test may give you insight on what to expect and the challenges you may face after your baby is born. The information provided by chorionic villus sampling may help prepare you for what lies ahead.
In the United States, all obstetrical practices will offer CVS or amniocentesis to women who are over the age of 35 – due to your increased risk of birth defect. However, women may also choose to get chorionic villus sampling in the following cases:
- Abnormal Result from a Prenatal Screening Test – If your first trimester screen was positive or abnormal, your doctor may recommend a CVS test to confirm a diagnostic, or rule out the problem all together. Keep in mind that many babies with abnormal screening test results are born perfectly healthy without any problems. (A screening test is just that – it screens. It does not diagnose.)
- Chromosomal Abnormality in a Past Pregnancy – You will be offered CVS testing or an amniocentesis if you’ve had a past pregnancy that was affected by a chromosomal abnormality, or if you have a child who has Down syndrome or a chromosomal disorder.
- Family History of Genetic Disorder – If there is a family history of a genetic disorder, or if you or your significant other is a carrier of a genetic disease, your healthcare provider may recommend CVS testing.
CVS or Amniocentesis?
Both an amniocentesis and CVS testing provide similar information. Both of these prenatal diagnostic tests will let you know if your developing baby has Down syndrome, cystic fibrosis, Tays Sachs disease, or a certain other genetic or chromosomal disorders. Because your risk of having a baby with genetic problems increases with age, many pregnant women over the age of 35 will be offered diagnostic testing during pregnancy.
The choice to have a prenatal diagnostic test is up to you, however, both of these tests do carry a slight risk of a miscarriage. However, women who are impatient to learn whether or not their unborn child has a genetic defect may opt to have CVS testing, since chorionic villus sampling is performed between 10 and 12 weeks of pregnancy and an amniocentesis will not be performed until the second trimester – typically between 15 and 17 weeks pregnant.
One of the limitations of chorionic villus sampling is that it cannot detect neural tube defects – like spina bifida. An amniocentesis can diagnose this, however.
Benefits of Chorionic Villus Sampling
The main benefit of CVS testing is that it’s performed in the first trimester, so if your baby does have a chromosomal abnormality, it is diagnosed early. This allows you to make the best decision for your pregnancy, and it gives you more time to prepare for your baby’s future needs.
If you have any questions about “Who’s my baby’s daddy?” CVS testing can also determine paternity of your unborn baby. Because chorionic villus sampling is a biopsy of placental cells, it can easily be used to identify the baby’s father – if you are unsure of whom it is. CVS testing is typically not used for this purpose, but it is one of the benefits.
Risks of Chorionic Villus Sampling
Because chorionic villus sampling is an invasive procedure, it does come with several risks. You need to weigh the risks versus the benefits before agreeing to CVS testing. The most common risks of CVS include:
- Miscarriage – The most common risk of a chorionic villus sampling procedure is miscarriage. Miscarriage estimates vary, but it can be as high as 1 in 100, or 1 in 200. This is 3 percent higher than with an amniocentesis. However, if you have a trans-abdominal CVS, you have the same miscarriage rate as an amniocentesis. It’s slightly more risky to have a trans-cervical CVS.
- Vaginal Bleeding – Another complication of chorionic villus sampling is vaginal spotting or bleeding after the procedure. CVS testing can cause small amounts of your baby’s blood to enter your bloodstream, which may cause complications, especially if are Rh-negative.
- Uterine Infection – In rare circumstances, you may experience a uterine infection after chorionic villus sampling.
- Defects in Baby’s Fingers and Toes – According to the Mayo Clinic, a few older studies have indicated that CVS testing can cause your baby to have missing toes and fingers. But the risk appears to only apply if you get tested before 10 weeks of gestation. Current research indicates that you shouldn’t have a problem if you have a CVS procedure at 11 or 12 weeks pregnant.
The risks of chorionic villus sampling depend largely on your doctor’s skill and experience and the ultrasound imaging technology he or she uses.
What Happens During Chorionic Villus Sampling?
The CVS procedure can be done at your obstetrician’s office, or healthcare provider’s office. You do not need to stay overnight at the hospital, unless there are problems that develop during the test. There are two types of chorionic villus sampling that can be performed – trans-abdominal and trans-cervical. Your healthcare provider should discuss which type is best for you in your individual circumstance.
During the CVS procedure, you will be asked to lie on your back and expose your belly. Your doctor will apply a special gel and use an ultrasound transducer to see your baby’s position on a TV screen, or monitor of some kind. The ultrasound will guide your healthcare provider during chorionic villus sampling.
- Transcervical CVS – During a transcervical chorionic villus sampling, your doctor will clean your vagina and cervix with an antiseptic. Next, your vagina will open using a device called a speculum. Your healthcare provider will insert a thin, hollow tube (called a catheter) through your cervix to reach your placenta. A small sample of chorionic villus tissue will be removed.Some women describe a transcervical CVS procedure similar to getting a Pap smear. You may have some discomfort and pressure, and you may bleed afterwards. Most women do not find it painful.
- Transabdominal CVS – If your doctor chooses to do a transabdominal chorionic villus sampling, he or she will clean your abdomen with an antiseptic. Next, a needle will be inserted a long, thin needle through your abdominal wall, into your uterus, and into your placenta. The syringe will remove a small amount of tissue.A transabdominal CVS doesn’t hurt, but you may experience a stinging feeling when the needle enters your skin, and when the needle reaches the uterus, you may notice some cramping.
A typical CVS procedure will take between 30 and 45 minutes, but a majority of that time is devoted to setting up the ultrasound. The placental tissue that is removed during this prenatal diagnostic test will be naturally replaced. In the unfortunate event that your doctor does not remove enough tissue, you may need to have a repeat procedure.
Although you shouldn’t have any complications afterwards, in the event that you experience heavy bleeding, a fever, or contractions, call your doctor right away.
A few days after your CVS procedure, your doctor will give you a follow-up ultrasound to make sure that your pregnancy is still doing fine. You will want to avoid having sex, lifting anything heavy, or flying in the two to three days after your procedure. Take it easy.