Skip to main content

Section 10 – What is amniocentesis?


Amniocentesis is a procedure during which an obstetrician removes a small amount (about 15 to 20 millilitres) of amniotic fluid from around your baby in your womb. The cells from your baby that are floating in this fluid can be tested in the laboratory to look at the chromosomes. Amniocentesis is usually done after 15 weeks of pregnancy.

Having an amniocentesis carries an additional risk of miscarriage which is likely to be below 0.5% (around 1 in 200) of pregnancies. The additional risk of miscarriage following amniocentesis in a twin pregnancy is around 1%  (1 in 100) of pregnancies.

A miscarriage is most likely to happen up to three weeks after the amniocentesis. No one knows why this happens or who it will happen to. It can happen whether or not your baby has a chromosomal change.

Because amniocentesis is a specialised procedure, you may not be able to have it done locally. Instead, you may be offered an appointment at a different maternity unit.

If you have an infection such as HIV, hepatitis B or hepatitis C, you may need extra information and advice from a doctor who specialises in infectious diseases before you decide whether to have amniocentesis.

Your midwife or obstetrician can explain the test to you. It is your choice if you want this procedure or not.

If you decide to go ahead with an amniocentesis, we will ask you to sign a consent form agreeing to the procedure before it is carried out.

Preparing for an amniocentesis

  • You can have breakfast or a light lunch before your appointment.
  • You will need a full bladder for the scan you will have before the amniocentesis. 
  • You may be asked to empty your bladder for the amniocentesis procedure itself.
  • You may be more comfortable if you wear loose clothing.
  • You can bring your partner or a friend with you for support during and after the procedure, but please do not bring children with you.
  • If possible, you should arrange for someone to drive you home.

Having an amniocentesis procedure

The procedure takes about 10 minutes and you will have it done as an outpatient, usually in the antenatal clinic. You will be awake for the procedure, and lying down.

You will have an ultrasound scan before the amniocentesis. This is to check the position of your baby and to look for the best place to take the sample of fluid from inside your womb. Your abdomen is cleaned with an antiseptic solution to reduce the risk of infection. The obstetrician inserts a needle through your skin and the wall of your womb, and then takes a small amount of fluid from around your baby. The obstetrician will be watching the ultrasound scan to guide the needle and so avoid getting close to your baby. You may find the test a little uncomfortable.

Occasionally the procedure cannot be done due to the position of the baby. If this happens, the obstetrician may suggest that the procedure is done on another day.

There is a small chance that the obstetrician will not be able to get any amniotic fluid from around your baby. This means the test cannot be done. The obstetrician may suggest that the procedure is done again on another day.

You will also be asked to give a blood sample so that the laboratory can be sure that the results they get from the amniocentesis are for your baby rather than for you.


What happens after the procedure?

After the procedure you should rest in the clinic for up to 30 minutes. You may have tummy cramps afterwards, rather like period pains.

If your blood group is Rhesus negative, you will be offered an injection of anti-D after the procedure. This is to reduce the chance of antibodies developing in your blood, which could happen if your baby’s blood group is Rhesus positive.

Some obstetricians may advise you to take things easy for a couple of days after the procedure and to avoid having sex, or doing any heavy lifting or strenuous exercise. You won’t need complete bed rest.

If you have any pain or discomfort, you can take a normal dose of paracetamol.

Most women are back to normal after two days.

What to look out for

  • Severe pain, which you can’t control by taking mild painkillers (like paracetamol).
  • Any bleeding or unpleasant discharge from your vagina.
  • Any fluid leaking from your vagina.
  • If you suddenly feel unwell and have a high temperature or flu-like symptoms.

These symptoms do not always mean there is a problem, but you may need further care and attention. For advice, please contact:

  • the clinic where you had the amniocentesis, or
  • your midwife