Chorionic Villi Sampling

Norm of Chorionic Villi Sampling

No detection of chromosome or genetic defects.

 

Usage of Chorionic Villi Sampling

Detection of genetic defects, chromosomal abnormalities, and acquired disorders in fetuses in women who are at high risk. Disorders such as beta-glucuronidase deficiency, hemophilia (factor VIII or IX), cystic fibrosis, mental retardation, Down syndrome, chromosome abnormalities, fragile X syndrome, beta-thalassemia, and Duchenne's muscular dystrophy; infections.

 

Description of Chorionic Villi Sampling

Chorionic villi sampling (CVS) consists of extracting a small amount of villous tissue directly from the chorion. This procedure can be performed at about 10 weeks of gestation and does not require in vitro culturing of cells because sufficient numbers are directly available in the extracted tissue. The procedure allows prenatal diagnosis at about 2 months of gestation rather than at nearly 5 months of gestation. This procedure is the method of choice for prenatal diagnosis in the first trimester of pregnancy.

 

Professional Considerations of Chorionic Villi Sampling

Consent form IS required.

Risks
Bleeding, hematoma, infection, intrauterine death, spontaneous abortion. Limb reduction defects may occur, possibly caused by vascular accident from decreased perfusion in distal portions of limbs or from thrombosis at the sampling site or from inadvertent amnion puncture resulting in either amniotic bands or loss of amniotic fluid, with subsequent compression and deformity. See also Amniocentesis and amniotic fluid analysis. CVS involves a slightly higher fetal loss rate than amniocentesis does, with most estimates ranging from 1% to 2%.
Contraindications
Morbid obesity, retroverted uterus with intervening bowel.

 

Preparation

1. Arrange for a laboratory technician to be present to evaluate the sample on location.
2. Must have complete family history.
3. Provide continuous fetal heart tone monitoring.
4. See Amniocentesis and amniotic fluid analysis.
5. See Obstetric ultrasonography.

 

Procedure

1. Transabdominal CVS:
   • a. The client is positioned supine.
   • b. Under ultrasonic guidance, a long 20-gauge needle is inserted percutaneously through the abdomen into villous tissue.
2. Transcervical CVS:
   • a. The client is placed in dorsal lithotomy position.
   • b. Under ultrasonic guidance, a malleable catheter is inserted through the cervix into villous tissue.
   • c. The perineum, vagina, and cervix are prepared with antiseptic solution.
   • d. A sterile speculum is placed into the vagina to allow visualization of the cervix.
   • e. The catheter is advanced through the cervix into the chorion frondosum under ultrasonic guidance.

 

Postprocedure Care

1. Suggest maternal serum alpha-fetoprotein (MSAFP) screening at 15–20 weeks of gestation.
2. See Amniocentesis and amniotic fluid analysis.
3. See Obstetric ultrasonography.