Clinical Services

Chorionic Villi Sampling (CVS)

Introduction
Chorionic villi sampling (CVS) has come to be regarded as a safe and effective diagnostic procedure for the diagnosis of fetal chromosome abnormalities and single gene disordersvery early in the pregnancy. CVS involves aspiration of a small amount of placental tissue for prenatal testing. Technically it is similar to amniocentesis, but it is performed at 10-12 weeks gestation, or at any time thereafter. Often the CVS procedure is chosen by parents who feel it is important to know as soon as possible that their baby will not have Down syndrome or certain other genetic disorders.

GLG was the first genetic clinic in Wisconsin to offer CVS. In fact, the first successful transabdominal CVS in the United States was performed at GLG in 1985. The GLG physicians combine the resources of substantial experience (over 2,000 successful CVS procedures) with an outstanding safety record.

Unlike most other prenatal diagnostic centers, GLG provides CVS as a fully integrated combination of clinical and laboratory services. At GLG, the CVS session begins with the physician geneticist meeting with the patient to obtain her family pedigree, past medical history, and pregnancy history. The geneticist then provides a detailed discussion of the CVS procedure. This includes discussion of technical details, of the small possibility of false positive or false negative results, and of the benefits and risks. CVS is compared and contrasted with amniocentesis. Some patients decide, after the discussion, to have CVS, while others opt for amniocentesis, or forgo invasive prenatal diagnosis. They may decide in favor of the BEST test or a genetic ultrasound examination at 16-18 weeks gestation.

GLG combines the CVS procedure with a genetic ultrasound is performed at 18 weeks gestation when features of the baby's face, brain, heart, stomach, kidneys, bladder, genitalia and other structures can be seen in excellent detail. The combination of the history and pedigree data, CVS laboratory results, and genetic ultrasound examination will detect over 70% of birth defects and genetic disorders. This includes Down syndrome and other chromosome disorders, major malformations, and more subtle disorders. It also excludes most fetal fluid disorders and movement disorders.

Description
CVS is a procedure for obtaining placental tissue for prenatal diagnosis. Chorionic villi cells are analyzed immediately after tissue culture to determine the fetal chromosome constitution. They can also be used for biochemical or molecular studies, if indicated.

Procedure
When a patient chooses to proceed with CVS, the physician geneticist examines the baby and uterine contents by ultrasound. If the fetal and uterine situation is suitable, the CVS procedure is performed. The physicians at GLG prefer the transabdominal over the transcervical approach. The needle is inserted under direct ultrasound guidance and is continuously observed. It is placed within the placental tissue and does not pass through the amniotic sac or near the baby. To the patient it feels quite like getting an injection, with little to moderate discomfort. The sampling procedure takes about 30 seconds; it is not necessary to use anesthetics. No special precautions are required before or after. Occasionally there is some transient cramping of the uterus; this is normal.

The studies on the villi in the laboratory are supervised and interpreted by the same geneticist who took the patient's history and performed the CVS procedure. This integrated approach with the geneticist involved in both the clinical and laboratory aspects of the CVS procedure provides continuity for the patient and is particularly helpful when the results are abnormal. When circumstances arise that require further discussion or examination, the follow-up is conducted with the same genetic doctor who initially saw the patient.

Indications
The most common indications include:
• advanced maternal age
• previous child with a chromosome abnormality
• familial chromosome rearrangement
• biochemical or molecular diagnosis of a familial genetic disorder

Risks
There is substantial evidence that the transabdominal approach is safer than the transcervical method. In our experience with transabdominal CVS, the miscarriage risk is similar to that for amniocentesis (approximately I in 1,000).

Several years ago there were reports from a few medical centers about an association of limb malformations with CVS. This occurrence of limb defects has been shown to be related to the timing of the procedure (before 10 weeks gestation). Recent follow-up studies in infants from over 170,000 CVS patients have failed to demonstrate these defects when the procedure was performed after 10 weeks.

At GLG, the CVS procedure is always followed up with a detailed ultrasound examination at 18 weeks gestation. We have successfully completed CVS and follow-up ultrasound examination for over 2,000 patients. We have not observed limb defects in our CVS patients. We have published information on the safety and the methods of the transabdominal approach in major medical journals.ss

Turn Around Time
Chromosome results from direct analysis become available one day after the CVS procedure. The turn around time for results of biochemical tests and molecular studies depends upon the specific assay. These tests usually require cultured chorionic villus cells and may require four weeks for completion. Many DNA tests are performed directly from chorionic villus cells without prior tissue culture, which means the results can be available in a few days.

CPT Codes
99244 - consultation, level 4
76815 - ultrasound, limited
59015 - chorionic villi sampling
88267 - chromosome analysis, CVS
88235 - tissue culture preparation