Amniocentesis

Published by Bupa's health information team, September 2008.

This factsheet is for women who are considering having an amniocentesis test, or who would like information about it.

Amniocentesis is a test carried out during pregnancy to detect specific abnormalities in a developing baby (fetus).

Your care will be adapted to meet your individual needs and may differ from what is described here. So it's important that you follow your surgeon's advice.

• About amniocentesis
• Preparing for your amniocentesis
• About the procedure
• What to expect afterwards
• Recovering from amniocentesis
• What are the risks?
• Further information
• Questions and answers
• Related topics
• Sources

About amniocentesis

Amniocentesis involves taking a small sample of the amniotic fluid surrounding the baby in your womb. The fluid is then tested in a laboratory.

Amniotic fluid contains cells and various substances from your baby that can provide information about its health and development.

Why have amniocentesis?

Amniocentesis is normally used to identify chromosome disorders, such as Down's syndrome (trisomy 21) and Edward's syndrome (trisomy 18).

If you have a family history of a specific disorder these can also be tested for. These conditions include:

• musculoskeletal disorders, such as Duchenne muscular dystrophy
• blood disorders, such as haemophilia, thalassaemia or sickle cell anaemia
• metabolic disorders, such as phenylketonuria

When is amniocentesis offered?

Amniocentesis is usually offered:

• if a screening test has suggested a high risk of a birth defect or of Down's syndrome
• for women over 35 who missed the initial screening test, as the risk of the baby having a genetic disorder increases after this age
• for women who have a history of certain disorders at birth in their family
• if there is a possibility of a genetic abnormality, for example women who have, or whose partner has, an inherited condition such as sickle cell anaemia
• to find out the baby's sex if a parent is a carrier of a sex-specific disease such as haemophilia or Duchenne muscular dystrophy (both of these are more likely to occur in boys)

When is amniocentesis performed?

Amniocentesis is normally performed between 15 and 20 weeks of pregnancy.

Rhesus disease

Amniocentesis is sometimes used to check whether a baby is at risk of rhesus disease. The rhesus system is a way of grouping blood. If your blood is rhesus-negative, and the baby's is rhesus-positive (which can only happen if the father is rhesus-positive), your immune system (the body's defence mechanism) may attack the baby's red blood cells with antibodies. This can cause anaemia or jaundice in the baby, or even death soon after the birth.

Amniocentesis will monitor whether there has been an immune response against the baby's blood and evaluate its health.

If your blood is rhesus-negative you will be given an injection of an antibody called anti-D after the amniocentesis. You may be offered further injections if necessary.

Preparing for your amniocentesis

Your surgeon or midwife will explain how to prepare for your test.

The test is usually done as a day case and takes from 10 minutes to half an hour. The test can be slightly uncomfortable so you may choose to numb the skin where the needle will be inserted with a local anaesthetic.

Your surgeon will usually visit you to discuss the test and ask you to sign a consent form. This confirms that you understand the risks, benefits and possible alternatives to the test and have given your permission for it to go ahead.

About the procedure

The surgeon will move an ultrasound device over your tummy to create an image of your womb on a monitor.

This allows your baby's position and the position of the placenta to be seen as clearly as possible. This helps to locate the best place to remove some amniotic fluid without damaging the placenta, the cord or your baby.

The surgeon will insert a long, thin, needle through the wall of your tummy and into the sac of fluid that surrounds your baby. You may feel a sharp stinging sensation when the needle pierces the amniotic sac but this should only last a few seconds. A small amount of fluid will be removed and sent to the laboratory for analysis.

The fluid that is removed needs to be as clear as possible. Sometimes the test will need to be repeated, such as when blood is present in the sample.

What to expect afterwards

Certain conditions (eg Down's syndrome and Edward's syndrome) can be identified within a couple of days.

For an analysis of other conditions it takes longer. It can take a laboratory two to three weeks to provide a final result. This is an anxious time for everyone involved and it's a good idea to keep occupied until the results come through.

For most women the test will give a very clear result that the chromosomes are normal or not, or for other conditions, positive or not. Occasionally a different condition is detected than the one originally looked for. Rarely your baby may still be born with a disorder when you have a normal result. A normal result doesn't exclude every disorder.

Before deciding to have an amniocentesis it's also worth thinking about what the results will mean to you.

If the results show that your baby has normal chromosomes and no other obvious problems this is reassuring. However, amniocentesis can't test for every disease or guarantee that your baby will be born completely healthy.

If the amniocentesis results are abnormal, you will need to make some informed decisions. These decisions should be based on the results of the amniocentesis and what they mean for you, your family and your unborn baby. There are a number of options to consider.

• Whether to continue with or terminate the pregnancy. If the baby has a severe defect, some women opt to end the pregnancy (therapeutic abortion). Others want time to prepare themselves and their family for the birth of a baby with health problems.
• Where to have the baby. For example, if the baby has a problem that may need surgery, it would be best to give birth at a hospital where surgeons are experienced in surgery for newborns.

These decisions may be difficult, and it's a good idea for you to discuss the issues with your partner, your family, your doctor and other health professionals before deciding to have an amniocentesis.

Recovering from amniocentesis

If you need them, you can take over-the-counter painkillers such as paracetamol or ibuprofen. Follow the instructions in the patient information leaflet that comes with the medicine and ask your pharmacist for advice.

What are the risks?

Amniocentesis is commonly performed and generally safe. For most women, the benefits of a clear diagnosis of any problem with their baby are greater than the potential risks. However, in order to make an informed decision and give your consent, you need to be aware of the possible side effects and the risk of complications of this procedure.

Side-effects

These are the unwanted, but mostly temporary effects of a successful treatment.

You may have some mild pain or cramps, like period pain, and spotting (light bleeding from the vagina) for a few hours afterwards. If you have any other symptoms such as feeling unwell, heavy bleeding or contractions you should contact your doctor immediately.

Complications

This is when problems occur during or after the test. Most women are not affected, but the risks of amniocentesis include those listed below.

• Injury to you or your baby from the needle - using ultrasound to guide the needle reduces this risk. Puncture of the placenta is the most common potential injury, but this usually heals without any further problems.
• You may develop an infection because the procedure has let bacteria into the amniotic sac, but this is very rare.
• There is a slight risk that your blood will be exposed to your baby's blood. This is only an issue if your blood is rhesus-negative and your baby's is rhesus-positive (see Rhesus disease). This risk is reduced when you are given an injection of the appropriate antibodies after your test.

In about one in 100 cases, one of these complications of amniocentesis leads to miscarriage.

The exact risks are specific to you and will differ for every person. Ask your surgeon to explain how these risks apply to you.

Further information

The Royal College of Obstetricians and Gynaecologists
020 7772 6200
www.rcog.org.uk

Midwives Information and Resource Service
0800 581 009
www.midirs.org

Related topics

• Routine care during your pregnancy
• Down's syndrome
• Paracetamol
• Ultrasound in pregnancy

Sources

• Amniocentesis: what you need to know. Royal College of Obstetricians and Gynaecologists. June 2006. www.rcog.org.uk
• Guidance on the use of routine antenatal anti-D prophylaxis for RhD-negative women. Technology Appraisal Guidance - No. 41. National Institute for Clinical Excellence (NICE). May 2002. www.nice.org.uk
• Amniocentesis and chorionic villus sampling. Royal College of Obstetricians and Gynaecologists. Guideline No 8, January 2005. www.rcog.org.uk
• Mujezinovic F, Alfirevic Z. Procedure-related complications of amniocentesis and chorionic villous sampling. Obstet Gynecol 2007;110:687-694. www.greenjournal.org

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: September 2008