Chorionic Villous Sampling

Dr Monica Pahuja

What are the generally accepted indications for chorionic villous sampling?

Chorionic villous sampling (CVS) is usually carried out between 11 and 14 weeks of gestation (but can be carried out up until full term in selected cases), and involves either transabdominal or transcervical aspiration or biopsy of placental villi.

Previously, only amniocentesis was available for accurate karyotype diagnosis. This was carried out between 15–16 weeks. CVS has moved the time of diagnosis earlier. The indications for CVS are:

  • maternal age 35 years and above;
  • high-risk result from first trimester screening;
  • presence of ‘soft signs’ during ultrasound scan;
  • familial genetic disorder;
  • maternal or paternal history of metabolic diseases, sickle cell anaemia or thalassemia;
  • previous pregnancy with a chromosomal abnormality;
  • parent with known translocation (5% of Down syndrome is caused by unbalanced translocation involving chromosome 21);
  • paternity testing.

What are the absolute contraindications for a chorionic villous sampling?

  • Maternal systemic infection.
  • Gestation earlier than 10 weeks.
  • Rhesus isoimmunisation.
  • Active bleeding.

What are the relative contraindications for a chorionic villous sampling?

  • Low-risk pregnancy of a genetic or chromosomal abnormality.
  • Multiple pregnancies. If CVS is abnormal, it will be unclear as to which foetus is affected.
  • If the patient has a bleeding diathesis or is on heparin, please contact the patient’s obstetrician for appropriate management. Heparin will need to be stopped 24–48 hours before the procedure.
  • Transcervical route of sampling: cervical polyps, fibroids, fundal placenta, retroverted uterus with posterior placement of placenta.

Are there any preprocedural requirements before chorionic villous sampling?

Amniocentesis can also provide information about a number of chromosomal and non-chromosomal abnormalities, and this information might be complementary to CVS.

Amniocentesis is carried out a few weeks later than CVS (see Amniocentesis).

CVS can be carried out earlier than amniocentesis, but carries a higher risk of miscarriage than other tests that screen for chromosomal or genetic abnormalities (no risk for nuchal translucency plus serum screening, 1:300 for amniocentesis and 1:100 for CVS).

In addition, the combined nuchal translucency and serum marker screening used in the first trimester is not a definitive test, but a statistical evaluation of the likelihood of one of three chromosomal abnormalities: Down syndrome, trisomy 13 and trisomy 18. It cannot predict the likelihood of genetically inherited disorders.

What are the adverse effects of a chorionic villous sampling?

  • Spontaneous miscarriage 1:100 (1%).
  • Pain and bleeding (7%).
  • Small risk of chorioamnionitis (lower abdominal pain, discharge or bleeding).
  • Amniotic fluid leakage (0.3–0.7%).
  • Transcervical route associated with increased risk of miscarriage, bleeding and sample failures.

If the patient complains of ongoing pains, bleeding, fluid leak or has signs of chorioamnionitis, then she should be referred back to the specialist who carried out the test for further clinical and ultrasound review to exclude any of the above conditions.

Are there alternative imaging tests, interventions or surgical procedures to a chorionic villous sampling?

Amniocentesis can also provide information about a number of chromosomal and non-chromosomal abnormalities and this information may be complementary to CVS. Amniocentesis is performed a few weeks later than CVS. Amniocentesis is not used to assist diagnosis of suspected genetic abnormalities.

CVS gives us more information than amniocentesis but carries a higher risk of miscarriage than other tests that screen for chromosomal or genetic abnormalities (no risk for nuchal translucency plus serum screening, 1:300 for amniocentesis, and 1:100 for CVS.

In addition, the combined nuchal translucency and serum marker screening used in the first trimester is not a definitive test but a statistical evaluation of the likelihood of one of three chromosomal abnormalities: Down syndrome, trisomy 13, and trisomy 18. It cannot predict the likelihood of genetically inherited disorders.

Useful websites:

NSW Health Centre for Genetics Education: Fact Sheet 26
www.genetics.edu.au/Publications-and-Resources/Genetics-Fact-Sheets/FactSheetDIAGNOSTICTESTSDURINGPREGNANCY.pdf/view

Women’s and Children’s Health Network
www.cyh.com/Default.aspx?p=1

Genetics in Family Medicine: The Australian Handbook for General Practitioners
www.nhmrc.gov.au/_files_nhmrc/file/your_health/egenetics/practioners/gems/sections/03_testing_and_pregnancy.pdf

Last saved on 30 September 2016.

Related articles