Amniocentesis: what it is, the risks and how long results take

Amniocentesis is a diagnostic test that can tell you for certain whether your baby has certain genetic conditions. Here’s what happens, the risks, and what to expect afterwards.

What is it?

The NHS says amniocentesis checks whether your baby has a genetic condition, including Down’s, Edwards’ and Patau’s syndromes, sickle cell disease, thalassaemia and cystic fibrosis. It is offered if, for example, you have a higher chance result from screening, a previous affected pregnancy or a condition in the family. CVS may be offered instead. It’s your choice whether to have it.

When is it done?

It’s usually done between 15 and 20 weeks, though it can be done later.

What happens?

An obstetrician does the test, usually in hospital, and it takes about 10 minutes.
Using ultrasound to guide them, they pass a thin needle through your tummy into the womb to collect some amniotic fluid.
The NHS says it may feel uncomfortable but should not be painful.
You can ask for a chaperone.

The risks

The NHS says the risk of miscarriage is 1 in every 200 pregnancies. It is higher with twins or more. Most miscarriages happen within 3 days but can happen up to 2 weeks later. The risk of infection is fewer than 1 in 1,000 procedures. The test may also increase the risk of passing HIV, hepatitis B or hepatitis C to your baby, so tell your team if that applies to you.

Your results

The NHS says results for Down’s, Edwards’ and Patau’s syndromes usually take around 3 working days. Results for other conditions take around 2 weeks. You’ll normally be told by phone or in person. If a result is a diagnosis, you’ll be offered a conversation with a specialist about your options, and ARC can support you whatever you decide.

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).

After the test

A tummy ache in the first day or two is normal, and paracetamol can help. Rest if you can, today and tomorrow. If your blood group is rhesus negative, you’ll be offered an injection. See rhesus negative and anti-D.

Contact your maternity unit if you have:

tummy pain that doesn’t get better with paracetamol
fluid leaking from your vagina
a high temperature, or feeling hot, cold or shivery
vaginal bleeding
contractions

If you can’t reach them, contact your GP urgently or call NHS 111. 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.

Questions people ask

Is amniocentesis painful?

The NHS says it may feel uncomfortable but should not be painful.

Can I go back to work the same day?

Many people rest for the rest of the day and the next. Ask your hospital for advice for your situation.

What if the result is not what I hoped?

You’ll be offered time to talk to a specialist and support. See what a higher chance result means.