Genetic testing – evaluating your baby’s chromosomes or genes for abnormalities – is commonly discussed at an early prenatal visit. If any of the relatives of the baby’s mother or father has genetic disorders like Down syndrome, cystic fibrosis, or sickle cell disease, among others, your healthcare provider or genetic counselor may suggest testing to determine if your baby could be affected as well. Testing options commonly include amniocentesis, chorionic villus sampling (CVS) or cell-free fetal DNA testing.
The decision to undergo genetic testing is a personal choice. To aid your decision-making process, Pregistry is providing a series of articles to provide you with an explanation of what each test is, when and why it might be recommended, and what the results mean.
This blog talks about Chorionic Villus Sampling or CVS.
All about Chorionic Villus Sampling (CVS)
Chorionic villi are projections of cells which comprise a majority of the placenta. These cells harbor useful information about your baby’s genetic makeup. During a CVS procedure, a sample of the chorionic villi is aspirated (drawn out through a syringe) from the placenta to test for chromosomal abnormalities such as Down syndrome, cystic fibrosis, etc. CVS is not able to detect neural tube defects such as spina bifida, which can be detected by amniocentesis.
CVS can be completed earlier in pregnancy than amniocentesis, optimally between 10 and 12 weeks.
Who should and should not have CVS testing?
CVS may be recommended if you had a positive prenatal genetic screening result, had a prior pregnancy with a chromosomal abnormality, are 35 years and older, have a known family history of certain genetic abnormalities or you or your partner are a genetic abnormality carrier.
CVS can be performed through the cervix (transcervical) or abdomen (transabdominal). Transcervical CVS may not be recommended in the presence of vaginal bleeding/spotting within the past 2 weeks, cervical infection, cervical stenosis (narrowing), vaginismus (vaginal muscle spasms), uterine position or uterine fibroids.
The transabdominal approach may be advised against due to the position of the uterus (severely tilted backwards), intestinal loops blocking the uterus and/or the position of the placenta. This could be seen in cases where the baby is covering the placenta on the back wall of the uterus.
As with amniocentesis, in cases of potential Rh incompatibility (mom is Rh negative and baby is Rh positive), CVS may not be recommended in order to prevent Rh sensitization complications following the procedure (see below).
Are there risks associated with CVS?
As with any procedure, CVS does have certain risks which include:
- Miscarriage: There is a 1 in 100 risk of miscarriage with CVS which is higher with the transcervical method versus the transabdominal approach. Additionally, the risk of miscarriage increases with a fetus that is small for its gestational age.
- Rh sensitization: At times, fetal blood cells can leak into the maternal bloodstream. If you are Rh negative and the baby is Rh positive, your blood cells may think your baby’s blood cells are foreign invaders. A medication called Rh immunoglobulin, will be given to you after completion of the procedure. This will prevent your body from producing antibodies that fight against the fetal blood cells. Your healthcare provider may obtain a blood test to determine if you have begun to create antibodies.
- Infection: Although rare, it is possible that the needle used during the procedure may introduce an infection into your uterus.
- Finger/Toe Defects: Older studies identified a risk of fetal finger/toe defects, however this seems to only occur when the CVS was performed prior to 9 weeks’ gestation. This finding led to the current recommendations to perform CVS between 10 and 12 weeks’ gestation.
What do the results mean?
Once the results of the CVS test are available, your healthcare provider or genetic counselor will discuss the results with you. If the results are uncertain, additional testing, such as an amniocentesis, may be recommended for a more definitive diagnosis. However, if the CVS returns a positive result, meaning an abnormality has been identified, it is rarely wrong.
Speak with your healthcare provider or genetic counselor if you are considering genetic testing and/or if you have additional questions about which test (amniocentesis, chorionic villus sampling, or cell-free fetal DNA testing) is best for you.