chorionic villus sampling (CVS, Chorionic villus biopsy [CVB])
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p243-245
2025-11-12
50
Type of test Cell analysis
Normal findings
No genetic or biochemical disorders
Test explanation and related physiology
CVS is performed on women whose unborn children may be at risk for life-threatening or significant life-altering genetic defects. This includes women who:
• Are older than age 35 years at the time of pregnancy
• Have had frequent spontaneous abortions
• Have had previous pregnancies with fetuses or infants with chromosomal or genetic defects (e.g., Down syndrome)
• Have a genetic defect themselves (e.g., hemoglobinopathies)
CVS can be performed between 8 and 12 weeks of gestation for the early detection of genetic and biochemical disorders. Because CVS detects congenital defects early, first-trimester therapeutic abortions can be performed if indicated.
For this study, a sample of chorionic villi from the chorion frondosum, which is the trophoblastic origin of the placenta, is obtained for analysis. These villi are present from 8 to 12 weeks on and reflect fetal chromosome, enzyme, and deoxyribonucleic acid content, thus permitting a much earlier diagnosis of prenatal problems than amniocentesis (p. 45), which cannot be done before 14 to 16 weeks. Furthermore, the cells derived by CVS are more easily grown in tissue culture for karyotyping (determination of chromosomal or genetic abnormalities). The cells obtained with amniocentesis take a longer time to grow in culture, further adding to the delay in obtaining results.
Potential complications
• Accidental abortion
• Infection
• Bleeding
• Fetal limb deformities
Procedure and patient care
Before
* Explain the procedure to the patient.
• Be certain that the physician has obtained a signed consent.
* Tell the patient that no food or fluid restrictions are necessary.
* Encourage the patient to drink at least 1 to 2 glasses of fluid before testing.
* Instruct the patient not to urinate for several hours before testing. A full bladder is an excellent reference point for pelvic ultrasound.
• Assess the vital signs of the mother and the fetal heart rate of the fetus before testing. These are baseline studies that should be repeated during and on completion of the test.
During
• Note the following procedural steps:
1. The patient is placed in the lithotomy position.
2. Samples of vaginal mucus may be obtained to rule out pre procedural infections (e.g., Chlamydia).
3. A cannula from the endoscope is inserted into the cervix and uterine cavity (Figure 1).
4. Under ultrasound guidance, the cannula is rotated to the site of the developing placenta.
5. A syringe is attached, and suction is applied to obtain several samples of villi.
6. As many as three or more samples may be obtained to get sufficient tissue for accurate sampling.
7. If ultrasound indicates that the trophoblastic tissue is remote from the cervix, a transabdominal approach similar to that described for amniocentesis may be used.
• Note that this procedure is performed by an obstetrician in approximately 30 minutes.
* Inform the patient that discomfort associated with this test is similar to that of a Pap smear.
Fig1. Chorionic villus sampling. Diagram of an 8-week pregnancy showing endoscopic aspiration of extraplacental villi.
After
• Note that Rh-negative women (who have not been sensitized to Rh incompatibility) receive RhoGAM. This procedure may be contraindicated for women with known preexisting Rh sensitization.
• Monitor the vital signs and check for signs of bleeding.
• Schedule the patient for an ultrasound in 2 to 4 days to con firm the continued viability of the fetus.
• Assess the vaginal area for discharge and drainage; note the color and amount.
*Assess and educate the patient for signs of spontaneous abortion (e.g., cramps, bleeding).
* Inform the patient how she can obtain the results from her physician. Make sure that she understands that the results usually will not be available for several weeks. (Results may be available much sooner at major medical centers that perform this test.)
* Educate the patient about how to identify and report signs of endometrial infection (vaginal discharge, fever, crampy abdominal pain).
* Inform the patient about genetic counseling services if needed.
Abnormal findings
Genetic and biochemical disorders
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