Chorionic Villus Sampling (CVS) is performed in women whose unborn child may be at risk for a life-threatening or life-altering genetic defect. This includes women who (1) are older than 35 years at the time of pregnancy, (2) have had frequent spontaneous abortions, (3) have had previous pregnancies with fetuses or infants with chromosomal or genetic defects (e.g., Down syndrome), or (4) have a genetic defect themselves (e.g., hemoglobinopathy).
Chorionic Villus Sampling can be performed at 8 to 12 weeks of gestation for early detection of genetic and biochemical disorders. Because Chorionic Villus Sampling detects congenital defects early, first-trimester therapeutic abortions can be performed if indicated and desired.
A sample of chorionic villi from the chorion frondosum, which is the trophoblastic origin of the placenta, is obtained for analysis. These villi in the chorion frondosum are present from 8 to 12 weeks on and are thought to reflect fetal chromosome, enzyme, and deoxyribonucleic acid (DNA) content. This permits much earlier diagnosis of prenatal problems than with amniocentesis, which cannot be done before 14 to 16 weeks. Further, the cells derived by Chorionic Villus Sampling are more easily cultured for karyotyping (determination of chromosomal and genetic abnormalities). Chorionic Villus Sampling requires significant experience to be performed safely. Although amniocentesis is the safer procedure, the cells obtained take longer to grow in culture, which further adds to the delay in obtaining results. At this later point, therapeutic abortion for severe genetic defects is more difficult.
Chorionic Villus Sampling Complications
Chorionic Villus Sampling may lead to any of the following complications:
- Accidental Abortion.
- Amniotic Fluid Leakage.
- Fetal Limb Deformities.
How is Chorionic Villus Sampling Performed?
Chorionic Villus Sampling is performed by an obstetrician. The procedure usually takes between 20 and 30 minutes to be completed. The following steps should be taken in considerations when performing the test.
- A full bladder is an excellent reference point for pelvic ultrasound. To maintain a full bladder, the mother is encourage to drink at least 1 to 2 glasses of water or any other fluid before the test and not to urinate for several hours before the test.
- The mother is placed in the lithotomy position, and a sterile speculum is placed into the previously cleansed vagina to visualize the cervix.
- A cannula is inserted into the cervix and uterine cavity.
- Under ultrasound guidance, the cannula is rotated to the site of the developing placenta.
- A syringe is attached, and suction is applied to obtain three or more villous samples to ensure sufficient tissue for accurate sampling.
- If ultrasound indicates that the trophoblastic tissue is remote from the cervix, a transabdominal approach similar to that described for amniocentesis may be used.
- If the mother has Rh-negative blood and the baby has Rh-positive blood, she may receive Rho(D) immune globulin (RhoGAM) because of the risk for development of maternal antibodies to the fetal blood cells, which could threaten fetal well-being.
- Vital signs the mother and the baby are collected before the test and monitored during and after the test.
- Ultrasound is performed in 2 to 4 days after the procedure to affirm the baby’s well being.
- The mother should learn to report any signs of abortion or endometrial infection. Signs of abortion include Camps, and Bleeding. Signs of infection include Fever, Vaginal Discharge, and Crampy Abdominal Pain.
Findings of Chorionic Villus Sampling
Using Chorionic Villus Sampling chromosomal, genetic, and biochemical disorders can be detected. Many chromosomal and genetic defects are identified by karyotyping and genetic mapping. Genetic counseling is a vital part of this sort of testing. If therapeutic abortion is an option, the religious, moral, and ethical aspects of this decision need to be considered.