What is CVS?

CVS takes a small sample of cells from the placenta to check your baby’s genes. Unlike screening, it is a diagnostic test: it can tell you if your baby definitely has the condition tested for. The NHS says CVS is not routine. It is only offered if there’s a high chance your baby could have a genetic or chromosomal condition. That might be because of a higher chance result from screening, a previous pregnancy affected by a genetic condition, or a family history such as sickle cell disease or cystic fibrosis. It’s your decision whether to have it.

When is it done?

The NHS says CVS is usually carried out between the 11th and 14th weeks of pregnancy, though it can be later if needed.

What happens?

  • It is usually done through the tummy (transabdominal). A thin needle is guided by ultrasound into the placenta. Less often, it is done through the cervix.
  • The test takes about 10 minutes, and the appointment about 30 minutes.
  • The NHS says it is usually described as uncomfortable rather than painful. You may have period-type cramps for a few hours afterwards.

The risks

The NHS says the chance of miscarrying after CVS is thought to be less than 1 in 200 for most pregnancies, and around 1 in 100 for multiple pregnancies such as twins. Other possible complications include infection, or needing a repeat test if the first sample wasn’t enough. Your team will talk these through before you decide. Because CVS carries a risk of miscarriage, the NHS says it is only offered if there is a high chance your baby could have a genetic or chromosomal condition.

Your results

The NHS says a rapid result is available in about 3 days, followed by a more detailed result after 2 weeks. If the rapid result and an earlier scan both suggest a condition, your doctor will talk to you straight away about your options. If the earlier scan was normal, the NHS suggests waiting for the detailed results before making decisions.

After the test

Your hospital will give you aftercare advice. As with amniocentesis, the NHS says to contact your maternity unit if you have:

  • bleeding or fluid leaking from your vagina
  • a high temperature, or feeling hot, cold or shivery
  • tummy pain that doesn’t ease

Call 999 if you have bleeding along with severe tummy pain, pain in your shoulder, or feeling sick, faint or dizzy, or if the bleeding is heavy.

Antenatal Results and Choices (ARC) offers free, non-directive information and support. Its helpline is 020 7713 7486, Monday to Friday, 10am to 5.30pm, with calls on Tuesday and Thursday evenings (8pm to 10pm) arranged by emailing info@arc-uk.org. You can also text 07908 683004 (UK only).

Questions people ask

CVS or amniocentesis: which is better?

It depends on timing and your situation. The NHS says amniocentesis is usually done between 15 and 20 weeks and can also cause miscarriage. Results come later, leaving less time to consider your options. See amniocentesis.

Will I need a rhesus injection?

If your blood group is rhesus negative, you’ll usually be offered an anti-D injection. See rhesus negative and anti-D.

Can I say no to CVS?

Yes. It’s your choice, and you can take time to decide.

Who can come with me?

Ask your hospital whether you can bring someone. Policies vary.

Read next

Sources: NHS: chorionic villus sampling (CVS); NHS: if antenatal screening tests find something; NHS: amniocentesis; NHS: vaginal bleeding in pregnancy.

This is general information based on NHS and other UK guidance. Every body is different, so speak to your midwife or GP if you’re unsure about anything.