Published: 25 October 2021
Pregnant women are offered amniocentesis or chorionic villus sampling (CVS) for prenatal diagnosis for a variety of reasons including a higher chance aneuploidy screening result, fetal structural anomaly, or a known risk of inherited genetic disease.
CVS is usually performed between 11+0 and 13+6 weeks of gestation. If required, CVS can be performed between 14+0 and 14+6 weeks’ gestation. Individualised counselling of the merits of CVS versus amniocentesis should be provided for women considering CVS during this time period. Amniocentesis, performed to obtain amniotic fluid for analysis, is usually offered from 15+0 weeks.
This guideline was developed as part of the regular programme of Green-top Guidelines, as outlined in our document Developing a Green-top Guideline: Guidance for developers (PDF), and prior to the emergence of COVID-19.
This is the fifth edition of this guideline.
Please note that the information provided in this update will be considered for update by the RCOG Guidelines Committee 3 years after publication, with an intermediate assessment of the need to update 2 years after publication.
Developer declaration of interests
Dr K Navaratnam: None declared
Professor Z Alfirevic: None declared.
- Women should be informed that the additional risk of miscarriage following amniocentesis or CVS performed by a skilled operator is likely to be below 0.5%.
- Amniocentesis should not be performed prior to 15+0 weeks gestation.CVS should be performed between 11+0 and 13+6 weeks; it should not be performed prior to 10+0 weeks gestation.
- Women with multiple pregnancies should be informed that the additional risk of miscarriage for twin pregnancy following CVS or amniocentesis performed by a skilled operator is around 1%.
- When an invasive test is considered, screening results for blood borne viruses, viral load and antigen test results should be reviewed and individualised risk of viral transmission should be discussed.
- Women considering amniocentesis or CVS should receive detailed counselling and pregnancy mapping by suitably trained healthcare professionals.
- Care for women who consent to have a CVS or amnioncentesis should be organised in accordance with National Screening Committee Standards.