Chorionic Villus Sampling

oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

Chorionic villus sampling (CVS) is an invasive diagnostic test which involves sampling the developing placenta late in the first trimester of pregnancy, to allow examination of the fetal karyotype and/or genotype. It is most commonly performed transabdominally, although it may also be performed transcervically prior to 13 weeks.

CVS is usually reserved for those women at increased risk of carrying a fetus with a chromosomal abnormality.

The aim of the procedure is prenatal diagnosis of chromosomal/single-gene abnormalities.

CVS is most likely to be used in the following situations:[1]
  • Advanced maternal age.
  • Past history of genetic/chromosomal abnormality.
  • Familial chromosomal rearrangement.
  • Biochemical/molecular diagnosis of a familial genetic disorder.

CVS cannot be used to screen for structural problems such as neural tube defects, which have no known metabolic or molecular basis (unlike amniocentesis). Women should have serum alpha-fetoprotein and other diagnostic tests to detect this condition.

Save time & improve your PDP on Patient.co.uk

  • Notes Add notes to any clinical page and create a reflective diary
  • Track Automatically track and log every page you have viewed
  • Print Print and export a summary to use in your appraisal
Click to find out more »

To transabdominal CVS:

  • Active vaginal bleeding
  • Infection

Transcervical route of sampling is also contra-indicated by:

  • Cervical polyps
  • Fibroids
  • Fundal placenta
  • Retroverted uterus with posterior placement of placenta

Previous or suspected neural tube defects should be investigated by biochemical and ultrasound markers.

  • CVS is usually performed between 11 and 13 weeks (11+0 and 13+6).[2]
  • Written consent should be obtained.
  • The placental sample is obtained either by ultrasound-guided transabdominal needle, or ultrasound-guided transcervical cannula aspiration or biopsy forceps
  • Results are usually obtained within 7-14 days (direct preparation one week, long-term culture two weeks).
  • CVS allows earlier diagnosis than with amniocentesis (which may only be safely conducted in the second trimester) and earlier opportunity to consider termination of pregnancy in the event of fetal abnormality.
  • Use of biopsy forceps rather than cannula aspiration for the transcervical route seems to make the procedure technically easier, and is preferred by patients and operators alike.[3]

Diagnostic accuracy of CVS is 97.5-99.6%, depending on the abnormality being screened for. It is slightly less accurate than amniocentesis because of placental mosaicism (the placenta can have populations of cells with different karyotype/genotype in about 0.8-1.6% of cases). If results from direct preparation are inconclusive then amniocytes need to be cultured.

  • Repeat procedures are required in 1-10% of cases, due either to laboratory failure, mosaicism, ambiguous results, insufficient sample or maternal cell contamination. The latter occurs more frequently in transcervical CVS (1.9%-3.8%).
  • In a low-risk population, background pregnancy loss is about 2%, and second-trimester amniocentesis increases this risk by a further 1%.
  • Miscarriage rates following CVS are higher than after second-trimester amniocentesis. However, there is some evidence to suggest this continues to improve over time, probably relating to improvements in technique.[4]
  • The increase in risk is significantly higher for transcervical CVS in terms of pregnancy loss and miscarriage.[5]
  • Transcervical CVS is more technically demanding than the transabdominal route and more likely to lead to sample failures and multiple insertions.[5]
  • On the whole, second-trimester amniocentesis is safer than transcervical sampling or early amniocentesis.[5]
  • Where early diagnosis is needed, transabdominal CVS is preferred to early amniocentesis/transcervical CVS.[5]
  • Where transabdominal CVS is not technically possible then transcervical CVS or second-trimester amniocentesis should be used.[5]
  • Amniotic fluid leakage 0.3-0.7%.
  • Vaginal bleeding 7% (higher for transcervical vs transabdominal route).
  • Sepsis (rare).

CVS at 8-9 weeks was reported to be associated with an increased incidence in limb deficiencies (oromandibular limb hypoplasia and isolated limb disruption) in the fetus following case reports. The association between limb abnormalities and early chorionic villus sampling is uncertain, as the abnormality rates were subsequently felt to reflect those in the non-CVS population; however, CVS is no longer performed prior to 10 weeks. This is in part due to the greater technical difficulties involved.

There appears to be no significant difference in long-term health outcomes between children who had transcervical CVS and those who had amniocentesis for prenatal testing. However, some believe CVS has distinct teratogenic effects.[6] There are reports of earlier CVS being carried out in exceptional circumstances, but there was higher fetal loss and a case of limb abnormality.[7]

Any benefits of earlier diagnosis with CVS must be carefully balanced against the greater risk of pregnancy loss compared with second-trimester amniocentesis. There appears to be no significant difference in long-term health outcomes between children who had transcervical CVS or amniocentesis for prenatal testing.[8]

Further reading & references

  1. Stranc LC, Evans JA, Hamerton JL; Chorionic villus sampling and amniocentesis for prenatal diagnosis. Lancet. 1997 Mar 8;349(9053):711-4.
  2. Amniocentesis and Chorionic Villus Sampling; Royal College of Obstretricians and Gynaecologists (June 2010)
  3. von Dadelszen P, Sermer M, Hillier J, et al; A randomised controlled trial of biopsy forceps and cannula aspiration for transcervical chorionic villus sampling. BJOG. 2005 May;112(5):559-66.
  4. Caughey AB, Hopkins LM, Norton ME; Chorionic villus sampling compared with amniocentesis and the difference in the rate of pregnancy loss. Obstet Gynecol. 2006 Sep;108(3 Pt 1):612-6.
  5. Alfirevic Z, Sundberg K, Brigham S; Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database Syst Rev. 2003;(3):CD003252.
  6. Brambati B, Tului L; Chorionic villus sampling and amniocentesis. Curr Opin Obstet Gynecol. 2005 Apr;17(2):197-201.
  7. Wapner RJ, Evans MI, Davis G, et al; Procedural risks versus theology: chorionic villus sampling for Orthodox Jews at less than 8 weeks' gestation. Am J Obstet Gynecol. 2002 Jun;186(6):1133-6.
  8. Schaap AH, van der Pol HG, Boer K, et al; Long-term follow-up of infants after transcervical chorionic villus sampling and after amniocentesis to compare congenital abnormalities and health status. Prenat Diagn. 2002 Jul;22(7):598-604.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Gurvinder Rull
Current Version:
Peer Reviewer:
Dr John Cox
Last Checked:
19/12/2013
Document ID:
1952 (v24)
© EMIS