Like amniocentesis, CVS can identify:
• Nearly all chromosomal abnormalities, including Down Syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). The test is more than 99 percent accurate in diagnosing these conditions.
• Several hundred genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. The test is not used to look for all of them, but if your baby is at increased risk for one or more of these disorders, CVS can usually tell you whether she or he has the disease.
Unlike amniocentesis, CVS cannot detect neural tube defects, such as spina bifida. If you opt for CVS, you'll be offered a blood screening test in your second trimester to determine whether you're at increased risk for neural tube defects. Most neural tube defects can be detected by a detailed second-trimester ultrasound done at a state-of-the-art academic center.
Be aware that if you perform a CVS, there's a 1 percent chance of seeing a result called a mosaicism, where some cell lines cultured from the placenta contain abnormal chromosomes and some are normal. If your CVS detects mosaicism, you will have to have amniocentesis and possibly other testing.
What are the risks of CVS?
Although it's often estimated to be between one in 100 and one in 200 — which is higher than the usual estimates for amniocentesis — there's no real consensus on the actual risk of miscarriage due to CVS.
One center that does a lot of CVS recently found the miscarriage rate from the procedure was down to about 1 in 360 — similar to the center's miscarriage rate from amniocentesis. This is most likely due to improvements in ultrasound imaging and the doctors' increased experience in doing CVS.
Because a certain percentage of women will end up miscarrying at this point in pregnancy anyway, there's no way of knowing for sure whether a miscarriage following CVS was actually caused by the procedure. Your particular risk depends in large part on the skill and experience of the doctor performing the procedure.
There has been some concern that CVS is associated with limb defects in babies, such as missing fingers or toes, but this was primarily seen in tests done on women before 10 weeks of pregnancy. Current research suggests that there is no increased risk for this problem in women who have CVS at 11 weeks or later.
Is there any way to reduce the risks of CVS?
Ask your practitioner or genetic counselor to refer you to an experienced doctor who does a lot of CVS procedures and who is expert at both the transabdominal and transcervical procedures, so she can choose the one that's safest for you. You may also want to ask about the estimated rate of procedure-related miscarriage for the doctor or the center where you're considering having the procedure done.
You'll also want to make sure that an experienced registered diagnostic medical sonographer provides continuous ultrasound guidance during the procedure. This greatly increases the chances that the doctor will be able to obtain enough tissue on the first try, so you won't have to repeat the procedure.
Can I meet with a genetic counselor before deciding whether to have CVS?
Yes. In fact, most testing centers require that you meet with a genetic counselor to discuss the risks and benefits of various methods of prenatal screening and testing before you have an invasive procedure like CVS .
The counselor will take down your family history and ask questions about your pregnancy. Your answers will enable the counselor to give you a sense of your risk for having a baby with chromosomal problems or a particular genetic disease. Then you can decide whether you want to be screened, go right for CVS or forgo testing altogether.
How can I decide what's right for me?
The American College of Obstetricians and Gynecologists now recommends that women of all ages be offered first- and second-trimester screening and diagnostic testing options. Your practitioner or genetic counselor should discuss the pros and cons of the available approaches with you. But ultimately, whether or not to test is a personal decision.
Many women opt for screening and then make a decision about diagnostic testing based on the initial results. Other women opt for diagnostic testing right away. (They may know that they're at high risk for a chromosomal problem or a condition that can't be detected by screening — or they may just feel that they want to know as much as possible about their baby's condition and are willing to live with the small risk of miscarriage to find out.) Some women will decide to have no screening or testing.
If you opt for screening first, you can then decide — with the help of your practitioner or genetic counselor — whether your results indicate a high enough risk that you want to have CVS. You'll need to weigh your need to know about your baby's condition against the small chance that diagnostic testing could cause a miscarriage.
Some women who opt for invasive testing are pretty clear in advance that they would terminate the pregnancy if a serious problem were found. Others may decide to have CVS even though they aren't sure what they'd do if they got bad news.
Some women may decide to have CVS even if they know they would never terminate a pregnancy. They may feel that finding out that their baby will have special needs will help them prepare emotionally for the challenges ahead. In certain cases, they may want to switch to a better-equipped hospital for post-birth support.
There are even are a few conditions that may be treated while the baby is still in the womb. So if there's a strong suspicion that your baby may have one of these rare problems, you might opt for CVS to find out. On the other hand, some women feel strongly about not having a procedure that increases their risk of miscarriage, especially if the results aren't going to affect the management of their pregnancy. So they decide not to have invasive testing.
There's no one right decision. Individual parents-to-be have different feelings about what risks are acceptable and may arrive at different conclusions when facing the same set of circumstances.
If I choose diagnostic testing, how do I decide between CVS or amniocentesis?
Both tests can tell whether your baby has a chromosomal problem or genetic disorder. CVS is done earlier in pregnancy (usually between 11 and 12 weeks), so you can find out sooner about your baby's condition. If everything's okay, your mind will be put at ease that much sooner. Or, if there is a serious problem and you opt to terminate the pregnancy, you'll be able to do so while you're still in the first trimester.
On the other hand, you may prefer to wait for the results from second-trimester screening before subjecting yourself to an invasive test. At that point, amniocentesis would be your only option.
Other considerations may influence your decision as well. For example, if you're at high risk for having a baby with a neural tube defect, you may want to have amniocentesis, as CVS cannot diagnose these defects.
Before making a decision, you'll want to discuss all of these issues with your partner, your health practitioner, and possibly a genetic counselor.
What's CVS like?
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. (Some testing centers do this when you come in for your CVS, while others do it in advance.) You'll need to have a full bladder in order to get a good view of your uterus on the ultrasound.
The goal of CVS is to obtain a tiny tissue sample from your placenta, which will be sent to a lab for analysis. The doctor will withdraw the sample through your cervix or abdomen, depending on which approach gives her best access to your placenta. A technician will use ultrasound to help guide the procedure.
If the doctor decides to go through your cervix, your vagina and cervix are first cleaned with an antiseptic to prevent any bacteria from entering the uterus. The doctor then threads a catheter through the cervix and uses gentle suction to get a sample from the placenta.
If the CVS is going to be done through your abdomen, the doctor first numbs a spot on your abdomen with a shot of local anesthetic. She then inserts a longer needle through your skin, muscle, and uterine wall to extract the sample.
Whether tissue is obtained through your cervix or abdomen, the amniotic sac won't be disturbed. When the test is done, the doctor will check your baby's heartbeat with an external fetal monitor or by ultrasound.
The procedure might hurt a little, but it's over relatively quickly. It takes no longer than half an hour from start to finish and the extraction itself takes only a few minutes. Women who've had a transcervical CVS say it feels similar to a pap smear, which may feel like a cramp or pinch. Those who have a transabdominal CVS may experience some discomfort in the abdominal area.
Note: If your blood is Rh-negative, you'll 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.
What happens after the procedure?
You'll need to take it easy for the rest of the day, so arrange for someone to drive you home. Avoid heavy lifting, intercourse, and air travel for the next two or three days.
Some cramping and light bleeding over the next day or so are both normal, but report them to your doctor or midwife anyway. If you have significant cramping or vaginal spotting, or you're leaking amniotic fluid, call your practitioner immediately. They could be signs of impending miscarriage. Also call if you have a fever, which could be a sign of an infection.
When will I get the results?
You should have the results of the chromosomal analysis in seven to ten days. During this period, the technicians at the laboratory culture the tissue cells (which have the same genetic makeup as the baby's cells) and allow them to reproduce for a week or two. They will analyze the cells for chromosomal abnormalities. You can also find out your baby's gender if you want to.
Testing for genetic disorders generally takes two to four weeks to show results. Some labs can give you some preliminary findings in two days. If that option is available, you'll have to make a special request to receive this speedy but more costly service.
What happens if my baby is found to have a problem?
You will be offered genetic counseling so that you can get more information and discuss your options. Some women may opt to terminate the pregnancy, while others will decide to continue.
Whichever route you choose, you may find that you want further counseling or support. Some women find support groups helpful, others may want individual counseling, and some may choose both. Be sure to let your practitioner and genetic counselor know if you need more help so they can give you the appropriate referrals.