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Amniocentesis is a diagnostic procedure carried out during pregnancy. It is most commonly used to check the baby’s chromosomes for specific disorders, such as Down syndrome known as (Mongol). In this condition the baby has an extra chromosome with a total of 47 instead of the normal 46 chromosomes. Amniocentesis is occasionally performed for other reasons; to test for other disorders in pregnancy such as infection or in cases of Rh incompatibility. It can be used later in pregnancy as well to test for fetal maturity. Although the procedure is the same, it may be done later and the amniotic fluid is analysed slightly differently. These tests look for substances in the fluid itself, rather than at the baby’s chromosomes
When and how is amniocentesis performed?
Amniocentesis should only be performed after 15 weeks. This is to reduce to risk of miscarriage or preterm labour. You do not usually need a local anaesthetic. Before the procedure, gel is applied over your abdomen. You are scanned to check the positions of both the baby and the placenta (afterbirth). Your skin is then cleaned with an antiseptic solution where the needle will be inserted.
The procedure is done under ultrasound guidance to ensure a safe distance from the baby, a fine needle is pushed into your skin, through your abdomen and womb. Usually the person doing the procedure will avoid the placenta. Sometimes the needle will go through the placenta as this might be the only way to get the fluid. This is unlikely to cause you or your baby any harm.
A small sample of the fluid surrounding the baby is removed using a syringe. This fluid should be an amber/yellow colour but may be stained with blood. This is not harmful but may affect the accuracy of the result. The needle is then taken out and the baby is checked on ultrasound to make sure everything is ok.
A small plaster will be put on your skin where the procedure was done. You will be kept under observation for 30 minutes before leaving the clinic. You should take it easy for a couple of days after the procedure. You may notice some ‘spotting’ of blood and cramping for a few hours afterwards. This is normal. If you experience any unusual symptoms immediately after the test, such as feeling shivery (as if you have flu), fluid loss, bleeding or contractions you should seek advice immediately. Most women say that having amniocentesis is uncomfortable rather than painful, a bit like a period pain. Women describe a sharp stinging feeling when the needle goes in and a feeling of pressure when the needle comes out. Women also say they feel anxious.
The amniotic fluid, which contains some of the baby’s cells, is sent to the laboratory for testing. For about 8 in every 100 women having amniocentesis, not enough fluid can be taken and the needle has to be re-inserted. This is usually due to the position of the baby. If a second attempt fails, you will be offered an appointment to have the procedure again on another day.
You will need an anti D immunoglobulin injection if your blood group is Rh negative, after the procedure to prevent you from developing antibodies against the baby’s blood cells. This may have an affect on future pregnancies.
What are the risks?
Every pregnancy carries a risk of miscarriage even without any intervention. As amniocentesis involves putting a needle through the wall of the womb, it may sometimes cause a miscarriage due to injury or infection in the womb. The additional overall risk of miscarriage from amniocentesis is approximately 1%. In other words, about 1 in every 100 women who have amniocentesis under ultrasound guidance after 15 weeks will miscarry.
There is a small risk, less than 1 in 1000 women who have amniocentesis, that the procedure will cause a serious infection. Infection can be caused by the needle puncturing the bowel, or skin contamination, but neither of these should happen if standard practices for amniocentesis are followed. Infection can also be caused if the needle is contaminated by the ultrasound gel or the ultrasound probe. These risks can be minimised by standard procedures to reduce infection, for example, by using sterile gel. The probe can be covered as well by a sterile plastic bag.
With an experienced clinician, the risk of blood stained amniotic fluid is less than 1% (that is, less than 1 in 100 tests). Clinicians who do amniocentesis often, rather than occasionally, seem to be slightly better at getting enough fluid at the first insertion of the needle, and may also have a lower risk of miscarriage. Therefore the procedure should only be attempted by clinicians who are experienced at ultrasound and invasive procedures as amniocentesis. They should be performing enough cases per year to keep their skills. Some authorities have recommended at least 20 per year to be allowed to carry on performing amniocentesis. Please do ask your obstetrician about his/her experience before attempting this procedure.
If are you are HIV positive and you decide to have amniocentesis, this might increase the risk of passing HIV on to your baby. You may be offered treatment with HAART (highly active antiretroviral therapy) if you are not already taking it. This reduces the risk of the HIV virus infecting the baby. If you carry hepatitis B or hepatitis C viruses, there is in theory a possibility that amniocentesis might increase the risk that you pass this onto your baby. There is not enough information to be sure about whether this risk is real or not. Please do discuss these issues with your doctor so you can both reach a decision about whether or not to proceed with amniocentesis.
Should I have amniocentesis?
Amniocentesis should not be done routinely to all pregnant women due to the risks mentioned above. You may consider amniocentesis If you had a screening test whether blood test or Nuchal translucency (measuring the fluid at the back of baby’s neck) or both combined, and the result was high risk. Women who had a previous pregnancy with a chromosomal abnormality or having relatives affected with a genetic syndrome could consider having amniocentesis. If you have not been offered a screening test especially if you are above 35 years, you may have the test. The presence of abnormalities of the baby on ultrasound examination is an indication to undergo the test as there may be underlying chromosomal abnormalities. Finally if you want to know for certain whether your baby is affected then amniocentesis should be done as all other screening tests are not 100% accurate.
What tests will be carried out?
There are two types of laboratory test which can be used to look at the baby’s chromosomes. Either performing a full karyotype where all the baby’s chromosomes are checked usually you will receive the result within 12-14 days. Recently a rapid test has been introduced in Egypt where the major chromosomal abnormalities are checked including Down syndrome (known as ‘trisomy 21′ caused by an additional chromosome 21), Edward syndrome (known as ‘trisomy 18′ caused by an additional chromosome 18) and Patau syndrome (known as ‘trisomy 13′ caused by an additional chromosome 13). Sex chromosomes can be checked as well. Results from this test are usually available after three working days.
How reliable are the tests?
The laboratory tests use different techniques to analyse the baby’s chromosomes. With the full karyotype test there is small chance, about 1 in 100, that it will not give a clear result. This could be because it was not possible to analyse the sample in the laboratory (culture failure) or that the sample was analysed and the test gave an uncertain result. Some samples may not be suitable for the rapid test. Even if the rapid test does not find a problem, the full karyotype may show an abnormality (not detectable with the rapid test) when the full results become available about two weeks later.
For most women the laboratory test will give a definite ‘yes’ or ‘no’ answer. The result will let you know, one way or the other, whether the baby has the disorder the test was looking for. However, if the result is not clear, it may be necessary to offer you a repeat amniocentesis, or other tests depending on the situation.
What will the results tell me?
The laboratory tests which look at the baby’s chromosomes are able to detect a range of disorders, but not all. Most women who have amniocentesis will have a ‘normal’ result; in other words, their baby will be born without the disorder(s) the test was looking for. Some women will be informed that the baby has the disorder that the test was looking for. Very occasionally women have amniocentesis to detect Down syndrome and another disorder is detected by the test.
A very few women will have a ‘normal’ result and yet in spite of this, they will have a baby born with the disorder tested for, or another chromosomal or genetic condition. A normal result does not exclude every disorder.
What are my choices if the results are abnormal?
If the results are abnormal, they will be discussed fully with you. For the majority of disorders, there is no treatment or cure. You will need to consider what is best for you and the baby. The choices available are either to continue with the pregnancy and use the information provided to prepare for the birth and aftercare of the baby. The second option is to end the pregnancy. If you decide to terminate the pregnancy, you will be given full information about what this involves. It will depend upon how many weeks pregnant you are when you make the decision. Ending the pregnancy may involve going into labour.
Making a decision about amniocentesis
Making a decision about having a diagnostic procedure during pregnancy, such as amniocentesis, can be difficult. You may have to make that decision either alone or with your husband. To help make the decision which is best for you, your doctor should discuss the following information with you:
- The types of laboratory tests available in Egypt.
- How reliable are the laboratory test(s)
- The risk of having an uncertain result and being offered a repeat procedure
- The risk of miscarriage from amniocentesis, including the risk in the hands of your obstetrician
- How long the results will take
- The disorder tested for in full details.
- What to do if baby is found to have the disorder.
In making a decision about amniocentesis, it is important you have enough time and that you feel supported in your final decision. You should be given time to talk through your options and to be able to request any further information. The final decision is yours. Only you can weigh up how much information you want about a disorder versus the slight risk that the procedure may lead to miscarrying a baby who may, or may not, have a disorder.
If you decide to have amniocentesis, then you will be asked to sign a consent form before the procedure is carried out. The consent form will include the risks outlined above as a confirmation that the procedure has been fully discussed with you before you attempt it.
Reference: Royal College of Obstetricians and Gynaecologists, patient information leaflet.