What Is Chorionic Villus Sampling (CVS)?

What to expect when undergoing this test

Chorionic villus sampling (CVS) is a prenatal test that checks for chromosome disorders or inherited diseases in a fetus, such as Down syndrome and cystic fibrosis. The test involves examining a sample of tissue from the placenta called chorionic villi, which share the same genetic make-up as the developing baby. The sample can be taken via the cervix or by inserting a needle through the abdominal wall. Both versions are done between weeks 10 and 13 of pregnancy.

If you're pregnant and considering chorionic villus testing, this overview will help you understand why this elective test is done, when doctors usually advise women to have it, what risks may be involved, what the procedure is like, and how to understand the results.

what to expect during a CVS
Illustration by Emily Roberts, Verywell

Purpose of Test

The goal of CVS testing is to determine if a developing fetus has certain defects, specifically:

This vital information can help prospective parents make important decisions, such as whether to continue a pregnancy that will result in severe birth defects or stillbirth, as well as how to prepare for the arrival of a child who will have special needs.

Chorionic villus sampling may be advised for women who:

  • Have had positive or worrisome results from a prenatal screening test such as the first-trimester screen or prenatal cell-free DNA screening
  • Have had a chromosomal condition such as Down syndrome in a previous pregnancy, which increases the risk of it occurring again
  • Are 35 or older, which puts them at increased risk of chromosomal conditions
  • Have a family history of a specific genetic condition, or whose partner is a carrier of a genetic condition, such as Tay-Sachs disease

CVS vs. Amniocentesis

New parents considering prenatal testing often make a choice between CVS and amniocentesis (often referred to as amnio). Both tests involve removing tissue from inside the womb (in the case of amniocentesis, amniotic fluid that contains fetal cells) and are considered equally safe.

CVS can be done somewhat earlier, however—typically between weeks 10 and 13 of pregnancy. Amnio is done between weeks 15 and 20, but has a distinct advantage over CVS in that it can detect neural tube defects such as spina bifida.

Risks and Contraindications

There are two ways to perform CVS: by obtaining a sample through the cervix (transcervical chorionic villus sampling) or by inserting a needle through the abdominal wall (transabdominal chorionic villus sampling).

Because both of these options are invasive, CVS carries certain risks. Some are more serious and, fortunately, rarer than others.

Common Risks

  • Cramping, usually during the test as the sample is being taken and sometimes for a few hours after. The cramps are similar to those you have during your period.
  • Bleeding: You may have some spotting for a few hours after a CVS test, but you should not have heavy bleeding.
  • Leaking of amniotic fluid

Rare Risks

  • Miscarriage: The risk of pregnancy loss after chorionic villus testing varies slightly according to the type of test. One 2016 study found that the miscarriage rate after transabdominal CVS is around 2.43 percent; after transcervical CVS, the pregnancy loss rate is 2.76 percent. According to the Mayo Clinic, the risk of miscarriage may be higher if a baby is smaller than normal for its gestational age.
  • Rh sensitization: Chorionic villus sampling can cause some of a baby's blood cells to enter the mother's bloodstream. If the baby is RH-positive (which means a protein called Rh factor is present on the surface of red blood cells) and the mother is Rh-negative, this can cause her body to produce antibodies to fight off what it perceives to be a danger. In turn, these antibodies can cross the placenta and cause serious health problems or even death in a fetus or newborn.
  • Uterine infection: Infection sometimes is the reason for miscarriage associated with CVS.
  • Limb defects in infants: Although highly unusual, this is most likely to happen when CVS is done very early (before 9 weeks).

    Contraindications

    CVS testing often is not recommended for women who:

    • Have a sexually transmitted disease or other infection
    • Are carrying multiples (twins or more)
    • Have had vaginal bleeding since becoming pregnant
    • Are Rh-negative but are carrying a baby that is Rh-positive (see above)
    • Have uterine fibroids
    • Have a tilted uterus

    CVS testing may not be advisable for women who:

    • Have a history of premature labor
    • Have an insufficient (incompetent) cervix
    • Have placenta previa (meaning the placenta is positioned low, near, or over the cervix)
    • Have abruption placentae (the placenta is separate from the uterine wall too early)
    • Are taking medication that can cause excessive bleeding

    Before the Test

    Chorionic villus testing requires little preparation on the part of a mom-to-be, but there are some factors to keep in mind that will help you get ready for your test.

    Timing

    Expect to spend a couple of hours at your CVS test appointment. It will take only about 10 minutes for the actual retrieval of chorionic villus cells, but you'll need to factor in time before the test to speak to your doctor so he can answer any questions you might have, as well as a few minutes to change out of your clothing.

    After the test, you and the baby will be monitored for about an hour. You probably will be advised to go home and rest for the remainder of the day, so you may want to plan to take the entire day off from work or other activities.

    Location

    Your CVS test likely will take place at your doctor's office in an exam room with ultrasound equipment. If you're being cared for by a midwife, she probably will have a relationship with a gynecologist she can refer you to for prenatal testing.

    What to Wear

    You'll be asked to undress from the waist down or completely and to put on a hospital gown, so you may want to wear clothing that is easy to slip on and slip off. Bring socks; exam rooms often are chilly.

    Cost and Insurance

    Your health insurance may cover at least some of the cost of a CVS test—particularly if you have certain risk factors such as an age over 35 or a family history of a genetic disorder. Policies can differ greatly, though, so be sure to check with your insurance company before scheduling your CVS.

    If you have to pay for CVS yourself, keep in mind that in addition to the cost of the procedure, there may be additional fees, such as for the lab work.

    What to Bring

    Bring your health insurance card in the event it's not on file at your doctor's office. In case of spotting after the procedure, you might consider slipping a mini sanitary pad or two into your bag. You also may want to have your spouse, partner, or a good friend or family member along for support. The person you bring will be able to be with you while the test is being done, if you'd like.

    Other Considerations

    Before having chorionic villus sampling, it can be helpful to speak with a genetic counselor, especially if you know there's a risk your child could have a genetic disorder. This will allow you to understand how high that risk really is and give you information that may be helpful as you make your decision about having CVS. Couples who are certain that they would not terminate a pregnancy under any circumstance may ultimately decide not to go through with CVS testing, for example. Or, they may want to know as much as possible ahead of time about the health of their baby so that they can be prepared. These decisions are very personal.

    Be aware that a CVS test will reveal the sex of your baby and that this information may be included on any written results you receive. If you don't want to know if you're having girl or boy ahead of time, make sure your doctor and/or genetic counselor know so that they don't inadvertently spill the beans.

    During the Test

    You may feel nervous or apprehensive about having chorionic villus sampling. This is normal. At least some of that anxiety may be relieved by learning as much about the process ahead of time as you can. Know, too, that the doctor and nurse who will help you through this process are there to explain everything and answer any questions you may have.

    Here's what you can expect whether you're having transabdominal CVS or transcervical CVS.

    Pre-Test

    You may be instructed to not empty your bladder the morning of the test. This is because a full bladder can make it easier for the doctor to guide the needle or catheter.

    Either way, after you arrive at your doctor's office and have checked in, he or she will talk to you about the procedure. You will then be given a few minutes to prepare.

    You will be given privacy to either undress from the waist down or disrobe completely and put on a hospital gown. A sheet or paper drape to cover the lower part of your body will be provided. You can leave on your socks if your feet feel cold.

    When you're ready, a nurse will have you sit on the exam table. She'll take your blood pressure and check your heart rate and breathing. At some point during this process or shortly after, the doctor will come in to begin the test.

    Throughout the Test

    Both transabdominal CVS and transcervical CVS rely on ultrasound to help the practitioner guide the needle, so regardless of which type of test you're having, the first step will be an ultrasound. The doctor will be double-checking the baby's gestational age to confirm that you are between 10 and 13 weeks pregnant and that it is a safe time to do CVS testing.

    The ultrasound also allows the doctor to locate the placenta in order to guide the needle correctly. For this procedure, your abdomen will be slathered with a cold, clear, water-based gel to make it easy for the transducer—a hand-held probe that picks up the sound waves that produce an image of the inside your uterus—to glide along your skin. You may be able to see (and hear) the baby's heartbeat on the ultrasound monitor, depending on how it's positioned in relation to the exam table.

    The doctor doing the test also may press down on your abdomen to find the position of your uterus. At this point, the steps of the procedure will depend on the type of CVS test being done.

    Transabdominal CVS: Because a foreign object (a needle) will be introduced into your body, your abdomen will first be cleansed with an antiseptic to help prevent infection. You also may be injected with a local anesthetic to numb your skin. If so, you'll feel a needle stick and, perhaps, a brief stinging sensation.

    Your doctor will then insert a hollow needle into your lower abdomen. The needle used for CVS is about the same thickness as one that would be used to draw blood from your arm, but somewhat longer. Using the ultrasound image on the monitor for guidance, the doctor will then guide the needle to the area of the placenta where the chorionic villi are located and draw a sample of cells up into the needle. You may feel brief cramping during this part of the procedure, but it will not be painful.

    After the cells have been collected, the doctor will gently slide the needle out and examine the sample to make sure enough cells were withdrawn. In very rare cases, the process will need to be repeated because the first sample didn't yield enough cells. If a transabdominal CVS has to be repeated a third time and there still aren't enough cells, you may be advised to have an amniocentesis when you are further along in your pregnancy instead.

    When the test is complete, excess ultrasound gel on your abdomen will be wiped away and the doctor or a nurse may put a small bandage on the site where the needle was inserted.

    Transcervical CVS: This is similar to having a Pap smear. You will be asked to place your feet into the stirrups of the exam table with your knees bent and your bottom close to the end of the table. The doctor will insert a speculum into your vagina; this instrument is made of either plastic or metal and is designed to hold the walls of your vagina apart so that the doctor as easy access to your cervix. The speculum will probably have a lubricant on it so that it slides in easily; if it's metal, it also may be warmed up. You'll feel some pressure and hear a clicking noise as the speculum is adjusted. It shouldn't hurt; speak up if it does—a smaller speculum may be necessary.

    With the speculum in place, your vagina and cervix will be cleansed with an antiseptic to help prevent infection. Then, a very thin catheter (tube) will be guided through your cervix to the chorionic villi. Cells will be suctioned through the catheter into a syringe. You may feel a pinch or cramping at this point. Again, you should not feel pain.

    Before withdrawing the catheter, the doctor will examine the syringe to make sure enough cells were taken for testing. If not, he or she may take another sample. Once enough tissue has been collected, first the catheter and then the speculum will be gently removed.

    The ultrasound gel on your abdomen and any leftover lubricant on or around your vagina will be wiped off.

    Post-Test

    After the sample has been taken, it will be sent to a special genetics lab. Meanwhile, your vital signs and the baby's heart rate will be checked again and monitored periodically for an hour or so. If you're Rh-negative, you may be given Rho(D) immune globulin to prevent your antibodies from reacting to Rh-positive cells from the baby.

    You will be allowed to get dressed and leave once your doctor feels that everything is stable with you and the baby.

    After the Test

    You may be advised to go home and rest for at least 24 hours. Don't do anything strenuous. You also shouldn't douche or have sex for two weeks after CVS testing, unless your doctor tells you otherwise. Your doctor may want to do a follow-up ultrasound a few days after your CVS just to make sure everything looks OK.

    Managing Side Effects

    You may experience some spotting or cramping after your CVS. You can use a mini pad to absorb bleeding. If your doctor says it's OK, you also might take an over-the-counter pain medication. If you don't want to take drugs, try a heating pad or warm bath to ease discomfort.

    The likelihood of any serious side effects after CVS testing is small, but there are some warning signs of potential complications to be aware of. If you experience any of these symptoms, let your doctor know right away:

    • Bleeding from your vagina (beyond spotting)
    • Bleeding or drainage of fluid from where the needle was inserted (if you had a transabdominal CVS)
    • Leaking of amniotic fluid
    • Fever and/or chills
    • Severe abdominal pain or uterine contractions (cramping)

    Interpreting Results

    It can take just a few days or as many as two weeks to get the results from a CVS test. Your doctor will call you to discuss them. If your CVS test comes back normal, it means that there are no signs of genetic disorders or chromosomal abnormalities in your baby. It's important to note that no test is perfect, but it should be reassuring to know that chorionic villus sampling is considered to be 99 percent accurate.

    If your test comes back abnormal, it will indicate which chromosomal or genetic abnormality your baby is affected by. For example, sickle cell anemia sometimes can be treated with stem cell therapy before a baby is born. And there are many ways to manage Down syndrome so that a child can live a full life. Other conditions, unfortunately, can result in severe birth defects or even be fatal.

    Although there are hundreds of disorders related to genetic or chromosomal problems, there are certain terms that often show up as part of the results of prenatal testing. Here are few common ones:

    • Trisomy: This term is used when a chromosome pair has an extra chromosome. For instance, trisomy 21, more commonly known as Down syndrome, occurs when there is are three chromosome 21s rather than two. Similarly, trisomy 13, an extra chromosome 13, causes a condition called Patau syndrome.
    • Translocation: Translocation occurs when two chromosomes that are not the same join together. An example of a disorder caused by a translocation mutation is Emanuel syndrome, in which there is extra genetic material from chromosomes 11 and 22 in each cell, causing features such an unusually small head, a small lower jaw, and ear abnormalities.
    • Mosaicism: With mosaicism, only some cells will have an extra copy of a chromosome.
    • Fractured chromosomes: This is the term used to describe when a chromosome breaks up in the cell culture, which could have health implications for the baby as an adult.

    Whatever your CVS test shows, it's vital that you sit down with your doctor or genetic counselor to discuss your options so that you can make an informed decision. You will want to find out, for example, about possible treatments for your child's disorder (either in utero or after he or she is born). It will be important to understand what sorts of special needs you can anticipate or what the chances are that the pregnancy may not be viable. You may also want to know more about your options regarding continuing your pregnancy or not.

    Follow-Up

    Sometimes CVS results will be unclear. The sample may not have been big enough to be thoroughly analyzed or the cells may not have cultured properly in the lab. If this happens to you, you may need to repeat the CVS test or have an amniocentesis.

    In addition, since CVS doesn't detect neural tube defects, you likely will be advised to have a blood test that can screen for them between 16 to 18 weeks.

    A Word From Verywell

    The decision to have chorionic villus sampling is yours. While it may be advised for you, women opt for it or out of it for a variety of reasons. Be sure to get whatever information you need from your doctor to make the best decision for you.

    There's no doubt that the prospect of having this test—and getting its results—can bring about some anxiety, especially if you have a known risk of having a child with a genetic disorder. But it should help to know that the vast majority of CVS tests do not cause complications and the vast majority of pregnancies are normal and result in happy, healthy babies.

    Keep in mind that if your CVS comes back abnormal, there are highly qualified genetic counselors and other experts who can help you decide how to proceed. Knowing that you're making choices regarding your pregnancy based on a full understanding of your situation and careful consideration on the part of your partner and yourself can go a long way.

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