Amniocentesis

Pregnant woman talking to a doctor across a table

Amniocentesis is a diagnostic test that will tell you if your baby has one of a number of genetic conditions, including Down’s syndrome. It’s done by taking a small sample of amniotic fluid from the womb via a needle and then testing it in the lab.

What does amniocentesis test for?

The test can give a firm diagnosis on the following conditions:

  • Down's syndrome
  • Edwards' syndrome
  • Patau's syndrome
  • Sickle cell disease
  • Thalassaemia
  • Cystic fibrosis
  • Muscular dystrophy
  • Tay-Sachs disease
  • Neural tube defects such as spina bifida
  • Rhesus disease
  • Infections

Why have I been offered amniocentesis?

You may be offered amniocentesis after routine screening, which usually consists of a combination of blood tests and a nuchal scan around the time of your 12-week scan. These routine tests give an indication of the likelihood of your baby having a abnormality or birth defect, but they can't give a firm diagnosis. If the results suggest the risk is high, you might be offered a diagnostic test such as amniocentesis to give you a firm yes or no answer.

I was given odds of 1 in 140, and I decided to have the test, because 20+ weeks of not knowing would have bloody killed me. I needed to know either way.

Older mothers may also be considered to be higher risk, so you may be given the opportunity to have additional screening if you’re pregnant over 40.

You might also be offered amniocentesis it if you or your partner has a family history of genetic disorders, or if you’ve had a genetic disorder in a previous pregnancy.

Do I have to have amniocentesis if I’m offered it?

You don’t have to have the test – it will be entirely up to you. You’ll be given lots of information on the risks and benefits to help you decide.

When should I have an amniocentesis?

Amnio is done between week 15 and week 20 of pregnancy, though in special cases it can be done slightly later. There is a higher risk of it causing problems before 15 weeks, which is why it’s usually done later.

What happens in an amniocentesis test? Serious-looking pregnant woman talking to a nurse

The test involves taking a very small sample of amniotic fluid from inside the womb, which is then sent off to a lab to be tested. The fluid contains cells from your baby, and it is these cells which will be analysed.

A sonographer will first set up an ultrasound to have a look at the baby and check where the best place is to take the fluid from. They may rub some anaesthetic gel into your abdomen to numb the pain a bit.

If you understand the process, you might feel more comfortable. The sonogram will show where the foetus is, so the doctor can avoid that area and insert the needle in a liquid pocket. I found that watching the process actually made me relax a bit since I understood exactly what was happening.

Then, guided by the sonographer’s ultrasound, the obstetrician will carefully insert a long, thin needle through your abdomen and into the womb where a small amount of amniotic fluid is taken. Once a sample is collected, it is sent off for analysis.

The sonographer will check the baby on ultrasound again after the procedure to make sure he or she seems to be OK. You’ll be monitored carefully for the hour after the amnio to check there is no heavy bleeding before being sent home to rest. The whole thing takes about 10 minutes.

In a small percentage of cases, not enough amniotic fluid is removed and so they have to put the needle back in.

Is amniocentesis painful?

You may feel a sting as the needle goes in. And, as it is removed, lots of women report feeling a slight dragging sensation – a bit like period pain. It’s more uncomfortable than painful though.

Recovering after amniocentesis

You’ll be advised to bring someone with you as driving after an amnio is not recommended. Having been monitored for up to an hour, you’ll be sent home and should rest for the remainder of the day.

You’re advised not to do anything strenuous for 24 hours, including lifting heavy things (such as children) or having sex. Many women like to take a day or two off but if you prefer, you should be fine to return to work or resume normal activities the next day.

You may experience a bit of mild pain or light bleeding after an amniocentesis – this is normal. However, if you experience any of the following you should call the midwives or the hospital where you had the test done straight away:

  • Persistent or severe pain
  • A temperature of 38°C or more
  • Shivering
  • Clear fluid coming from the vagina
  • Contractions

What are the risks of amniocentesis?

It’s a fairly low-risk procedure and is carried out by experts in the field who do this all day long, so they are usually well-practised and hugely experienced.

amniocentesis procedure on pregnant woman
  • In approximately one in 100 cases a miscarriage occurs. It’s not known precisely why this happens but is thought to be caused by infection or damage to the amniotic sac.

There are a few other risks to consider, too, though they are minimal or easily remedied.

  • It’s possible that, if your baby is rhesus positive and you are negative, you can be sensitised to your baby’s blood. For this reason your blood will be tested beforehand so you can be given an anti-D injection afterwards.
  • There’s an increased risk of the baby developing club foot if the test is carried out before 15 weeks, which is why it’s not usually done until later on.
  • As with all surgical procedures, there is always a risk of infection but this risk is low (about one in 1,000).

Does amniocentesis cause miscarriage?

It is one of the risks (see above) but it’s a small risk – about one in 100 women who have amniocentesis will have a miscarriage. However, not all of those miscarriages will have been ‘caused by’ amniocentesis for certain – they may have happened anyway. Estimates vary, but some evidence suggests that actually only one in around every 900 women has a miscarriage as a direct result of amniocentesis.

Are there alternatives to amniocentesis?

There are a couple of other options available:

  • CVS, which is done between weeks 11 and 16, has a slightly higher risk of miscarriage (1-2%) but because it can be done earlier it gives you a bit longer to decide what to do if the results are positive.

A sample of chorionic villi cells is taken from the placenta using a needle, which is either inserted through the abdomen or through the cervix. The chorionic villi attach the placenta to the wall of the womb. They are made from part of the embryo that separates during early cell division and so they have exactly the same DNA as the foetus.

  • NIPT (non-invasive prenatal test) is not yet widely available on the NHS but is being piloted in some areas and it is possible to have the test done at a private clinic using a number of laboratories, both here and overseas. One of the most widely used is called ‘Harmony’.

NIPT is a maternal blood test done after 10 weeks and there is no risk at all to the baby. It can test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome. It does not claim to be 100% accurate but Antenatal Results and Choices says that if the result is ‘low risk’ then the baby is extremely unlikely to be affected. If it is ‘high risk’ you will be offered amniocentesis or CVS but it is then extremely likely that the diagnostic test will confirm the presence of a genetic disorder.

When will I get results from an amniocentesis?

For tests such as those for Down’s syndrome, you will usually get the results after around three days. Tests for the slightly rarer conditions may take two to three weeks. Waiting for results can be stressful so take it easy as much as you can and be kind to yourself at this time.

What if my amniocentesis is positive?

If the results come back and show that your baby does have one of the conditions or abnormalities tested for, it can come as a huge shock and leave you feeling worried for your baby and bereft of a specific imagined future.

It may mean you have big decision to make about whether to terminate the pregnancy, and your hospital will be able to put you in touch with experts who can help you to decide what is best.

If you decide to terminate, the method used will depend on your stage of pregnancy and the doctors and midwives will be able to tell you more about that. No one can make this sort of difficult decision for you, but there is lots of advice and support out there, from organisations such as ARC (antenatal results and choices) to the Mumsnet Pregnancy Choices Talk boards.

The results might also be an opportunity to prepare yourself and your family for your baby’s arrival. Knowing what sort of care they might require at birth and beyond can enable you to start putting that in place early on.

There are many help groups in operation who will be able to offer specific advice and support, such as The Down’s Syndrome Association. Mumsnet also has information on giving birth when your child has been diagnosed with a genetic condition or abnormality.

Can amniocentesis be wrong?

On the conditions and abnormalities it tests for, amniocentesis is pretty accurate (98-99%), though it's worth remembering that there are other conditions that it can’t diagnose. Amnio can also tell you the sex of your baby with near certainty, too, so do remember to tell your doctor if you don’t want to know this as it is sometimes included in the results you are sent.

Mumsnetters' experiences of amniocentesis

“I was immensely reassured by the amnio. It helped me bond with the pregnancy and accept that things were OK. I chose to find out the sex, too, which also helped. I took it easy for a few days, and didn't have cramping at all.”

“What struck me most in the past week since the results came back, is although I'm not having a child with Down's or a neural tube defect, there are a million other genetic defects that cannot be tested for. I thought that the amnio would give me ALL the answers and it doesn't. Some days I just walk around in a panic, worried about all the things that can't be tested for. I thought a good amnio result would leave me feeling elated but I just worry more.”

“I had a tough time with tests – nuchal, CVS and amnio. Just thinking of the stress makes me feel stressed now. Whatever your stats, if you decide to have the test then be kind to yourself, take extra special care of yourself and if possible have someone with you when you get the results. I had to wait nearly five weeks for the all clear but during this time I was the least worried as I could only wait. There was nothing else to do – it was a sort of break in the process.”