What is Chorionic Villous Sampling?: Chorionic villous sampling (CVS) is a procedure that involves taking a microscopic biopsy from the placental tissue, outside the sac where the fetus develops.  This tissue can then be used to detect chromosomal disorders such as Down syndrome, Trisomy 13, Trisomy 18, and other chromosomal abnormalities; or genetic abnormalities such as cystic fibrosis. 

Chorionic villous sampling is usually performed between 10 and 12 weeks gestation (10 to 12 weeks after the first day of your last menstrual period). 

Chorionic villous sampling is not a “routine” test, since there is some small risk associated with the test.  Generally, it is offered to patients who have an increased chance having a baby with a problem that can be detected by the procedure.  Your obstetrical caregiver will determine, during prenatal care, whether you are at increased risk for any of the problems that can be detected by CVS and, if so, may refer you to Rocky Mountain Perinatal Associates to find out more about the risks and benefits of the test.

Who is a candidate for CVS?: As mentioned above, CVS is usually offered only if there is a higher than expected risk of chromosomal or genetic abnormalities.  Common situations in which CVS may be offered include (but are not limited to):  

•  Maternal age: Currently, all patients are offered screening tests for chromosome abnormalities such as Down Syndrome, as described below. However, since the risk of chromosome abnormalities increases with maternal age, some older patients elect, after counselling, to skip the screening test, and have a definitive diagnostic test such as CVS. 
• Prior obstetric history: If a woman has had a prior child with certain types of chromosomal abnormalities or genetic defects, the recurrence risk may be enough to warrant definitive testing in subsequent pregnancies by chorionic villous sampling.
• Family history: If there is a family history of genetic defects, the recurrence risks may be enough to warrant offering definitive prenatal diagnosis with each pregnancy.  Not all genetic or other birth defects can be diagnosed before birth, so counseling is generally required in these situations to determine of a patient is a candidate for testing.  
• Abnormal “screening” tests: All pregnant patients are offered the option of having screening tests for Down syndrome, Trisomy 13 and Trisomy 18. One of these tests can be done at 11-12 weeks, and the results can determine whether a patient is a candidate for further testing by CVS.  Screening tests do not determine whether the fetus has the disorder in question; rather, they predict a risk level or probability of a baby having one of these abnormalities(for example the risk may be 1:10, or 1:100, or 1:10,000, or anywhere in between).  The risk level predicted by the screening test is then used to determine whether more specific, definitive diagnostic testing via techniques such as chorionic villous sampling would be warranted.  
  

How is CVS performed?: First, an ultrasound will be performed to determine that you are at the correct gestational age, as well as to determine the position of the placenta.  The microscopic biopsy of the placenta is then obtained, using ultrasound guidance, by either placing a very thin plastic “catheter” (see diagram) through your cervical canal (a”transvaginal” approach), into the base of the placenta, or by inserting a thin needle through the skin and wall of your lower abdomen, through the wall of the uterus, into the base of the placenta (a “transabdominal” approach).  If the transvaginal approach used, the procedure is relatively painless, with, at most, mild cramping, and the discomfort of the speculum that is used, as for a routine pelvic exam.  There is a bit more cramping involved if the transabdominal procedure is used,but this is generally well tolerated and lasts only minutes.  

Which of these approaches is used depends on the position of the placenta and the position of the uterus and cannot be determined until the ultrasound is performed.  

After the procedure, the physician will look at the specimen under the microscope to be sure that enough material is obtained to do the required testing. If a transcervical approach is used, there is greater than a 95% chance that enough tissue will be obtained.  Only one transcervical attempt will be made; if insufficient tissue is obtained, an additional, transabdominal procedure may be required.  If a transabdominal approach is performed, there is about a 5-10% chance that a second attempt will be necessary to obtain enough tissue.

How long do test results take?:  Generally, the complete diagnostic test results require about 7 to 14 days.  The staff of Rocky Mountain Perinatal Associates will notify you immediately when these results are available.

Are there any limitations for me after the procedure?  Usually, we would recommend against any strenuous activities, such as a strenuous workout regimen or physically demanding work, on the day of the procedure.  Patients can return to their normal, usual activities on the following day.  If a patient were to experience significant vaginal bleeding, worsening abdominal pain, fever, or anything that seems like leakage of fluid vaginally, she should notify her obstetrical caregiver or Rocky Mountain Perinatal Associates immediately.  Fewer than 5% of patients undergoing testing experience such symptoms. 

What are the risks of chorionic villous sampling?  If a patient has an chorionic villous sampling performed, there is a slightly increased risk of complications that could result in miscarriage.  It is important to remember that women between 10 and 12 weeks of pregnancy have an approximately 5% risk of miscarriage, even if they do not have such a procedure.  The additional risk of miscarriage if they undergo a chorionic villous sampling is usually predicted to be about one out of two hundred. As physicians have gained experience with chorionic villous sampling over the last several years, the risks have been estimated to be even lower, perhaps 1:300 or less.  Generally, the risk of miscarriage due to chorionic villous sampling, though low, is still felt to be slightly higher than that of amniocentesis, which is another test that can detect genetic and/or chromosomal abnormalities.  The advantage of chorionic villous sampling is that it can be performed more than a month earlier than an amniocentesis, which is generally performed at 15 weeks or later in pregnancy.  

Many years ago, there was a concern that chorionic villous sampling might increase the risk of what has been described as limb defects, such as missing or shortened fingers or toes.  When this data was analyzed, it was found that these risks were increased when chorionic villous sampling was performed at less than 10 weeks gestation.  When chorionic villous sampling is performed at or later than 10 weeks gestation, there is no increased risk of these abnormalities, compared to the general population.  

All of these risks will be discussed with you in detail by the staff at Rocky Mountain Perinatal Associates if your obstetrical caregiver feels that you may be a candidate for the procedure.