Published by Bupa's Health Information Team, October 2010.
This factsheet is for women who are considering having an amniocentesis test, or who would like information about it.
Amniocentesis is a procedure that involves testing the amniotic fluid to detect genetic abnormalities in a developing baby (fetus).
You will meet the doctor carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.
Amniocentesis involves taking a small sample of the amniotic fluid surrounding the baby in your womb. This fluid is then tested in a laboratory.
Amniotic fluid contains cells and various substances from your developing baby that can provide information about his or her health and development.
Amniocentesis is usually used to identify chromosome disorders, such as Down's syndrome (trisomy 21) and Edward's syndrome (trisomy 18).
Chromosomes are structures that contain genes - these contain the instructions for life and are inherited from parents. Normally, our cells contain 46 chromosomes: 23 inherited from each parent. Sometimes a mistake is made during cell division. This is most likely to occur when the sperm or egg is being formed and can cause there to be more chromosomes present. Most people who have Down's syndrome have an extra chromosome 21 and most people with Edward's syndrome have an extra chromosome 18.
Amniocentesis can sometimes be used to test for other conditions as well. If you get an infection during pregnancy, such as cytomegalovirus (CMV), amniocentesis can detect if the baby has also been infected. The procedure may also be done if you have a family history of a specific condition. These conditions include:
You will usually be offered amniocentesis if:
Amniocentesis can also be used to find out the baby's sex. This is important if you or your partner 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).
Amniocentesis is sometimes used to check whether your baby is at risk of rhesus (RhD) disease. As well as the blood groups A, B, AB and O, RhD is another way to categorise the type of blood you have. You will either be RhD-positive or RhD-negative - this means respectively that you carry the D antigen on your red blood cells or you don't. An antigen is a type of protein that can cause your immune system to react. If your immune system doesn't recognise an antigen, it will produce antibodies to attack it. Antibodies are proteins produced by your immune system that usually fight against viruses and bacteria.
Your baby won't necessarily have the same blood type as you. Therefore, you may be RhD-negative but your baby may be RhD-positive. If this happens and your blood comes into contact with your baby's blood, your immune system will react to the RhD antigen on your baby's blood cells and make antibodies against it (anti-D antibodies). These antibodies can then cross into your baby's bloodstream. This is called sensitisation and can cause problems for your baby (for example, anaemia).
Amniocentesis can monitor whether your immune system has reacted against your baby's blood and give more information about his or her health.
If your blood is RhD-negative, you will usually be given an injection of an antibody called anti-D after amniocentesis. This is because during amniocentesis there is a risk that some of your baby's blood may enter your bloodstream, causing your body to make anti-D antibodies. The injection helps to stop your immune system from reacting to your baby's blood but it won't harm your baby. You may be offered further injections if necessary.
Amniocentesis is usually done after 15 weeks of pregnancy, when you're in your second trimester.
Before deciding to have an amniocentesis, it's 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 show there is a problem, you will need to make some decisions. These will be based on what the results of the amniocentesis mean for you, your family and your unborn baby. You will need to think about several things including:
These decisions may be difficult, and it's a good idea to discuss the issues with your partner, family, doctor, genetic counsellor or your midwife before deciding to have an amniocentesis.
Your doctor or midwife will explain how to prepare for your test.
Amniocentesis is usually done as a day case and can take up to half an hour. The test can be slightly uncomfortable so your doctor may use a local anaesthetic to numb the skin where the needle will be inserted.
Your doctor will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen, and you can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead, which you may be asked to do by signing a consent form.
Your doctor will use an ultrasound device to check the position of your baby and the placenta in your womb. An ultrasound uses sound waves to produce an image of the inside of part of your body. This helps to find the best place to remove some amniotic fluid without damaging the placenta, the umbilical cord or your baby. Your doctor will use ultrasound throughout the procedure to monitor your baby.
Your doctor will insert a long, thin, needle through the wall of your abdomen (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 testing.
The fluid that is removed is usually an amber or yellow colour. Sometimes the test will need to be repeated, for example if there is blood in the sample.
If you need them, you can take over-the-counter painkillers such as paracetamol. Follow the instructions in the patient information leaflet that comes with the medicine and ask your pharmacist for advice.
Certain conditions (for example, Down's syndrome and Edward's syndrome) can be identified within a couple of days of amniocentesis.
For other conditions it can take a laboratory two to three weeks to provide a final result.
For most women the test will give a very clear result as to whether or not the chromosomes are normal, or for other conditions, positive or negative. Occasionally a different condition is detected than the one that was originally being checked for. Rarely, your baby may be born with a disorder despite you having a normal result.
Amniocentesis is commonly performed and generally safe. For many 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 are the unwanted but mostly temporary effects you may get after having the procedure. 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 side-effects such as feeling shivery and unwell, heavy bleeding or contractions, contact your doctor immediately.
Complications are when problems occur during or after the procedure. Most women are not affected, but the risks of amniocentesis include the following.
In about one in 100 women, one of these complications of amniocentesis leads to miscarriage.
The exact risks are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.
For answers to frequently asked questions on this topic, see Common questions.
For sources and links to further information, see Resources.
See a private GP in confidence to discuss any concerns you may have about your health or your family's health. Call 0845 600 3458 quoting ref. HFS GP.
You can't put a value on your health. Bupa Health Assessments help you identify any current or potential health risks, meaning you can take action about them now. Compare our range of health assessments or call 0845 600 3458 quoting ref. HFS100.
This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the About our Health Information page.
Publication date: October 2010
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