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Amniocentesis Test
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INTRODUCTION
This leaflet has been written to provide you with information about the amniocentesis test. This test is not offered as a matter of routine. It is used most often to test for Down’s syndrome, the commonest of the chromosome disorders. Less commonly it may be used to test for other specific genetic disorders.
WHO SHOULD CONSIDER AMNIOCENTESIS?
The final decision about having any test in pregnancy is yours but the following women may consider amniocentesis:
- Women with a high-risk result from a triple blood test, (sometimes called a serum screen ) which is designed to find out the risk of having a baby with Down’s syndrome.
- Women who have a potential problem found on the ultrasound scan, which may suggest a chromosomal abnormality.
- Women who have had a pregnancy or a child affected by a genetic condition that can be tested for by an amniocentesis.
- A couple who have had a baby with a chromosomal abnormality such as Down’s syndrome.
- Those who have a family history of genetic disorders including some rare inherited diseases.
- Women aged 36 years and over who have missed the screening tests for Down’s syndrome.
The chance of having a baby with Down’s syndrome gets higher as the mother gets older, as shown in the following table:
YOUR AGE CHANCE OF HAVING
A BABY WITH DOWN’S SYNDROME
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25 1 in 1500
30 1 in 910
35 1 in 380
38 1 in 190
40 1 in 110
45 1 in 30
WHAT ARE THE PROBLEMS ASSOCIATED WITH AMNIOCENTESIS?
Amniocentesis has now been available for a number of years and in Britain over 15,000 women have the test performed every year, so we know a lot about its safety and accuracy. We know that the test can sometimes cause a miscarriage and approximately 1 in every 100 women who have the test will miscarry as a result of the procedure. There is no evidence that the procedure itself harms your baby as the test is carried out under ultrasound guidance.
IS THE AMNIOCENTESIS TEST RELIABLE?
No test is absolutely perfect, but the chromosome test for Down’s syndrome is very reliable. It fails to give a clear result in less than 1 in 1000 cases. If you are having the amniocentesis for other genetic disorders, you should discuss the accuracy of the test with your genetic doctor or counsellor.
WILL THE TEST TELL ME ABOUT ANYTHING OTHER THAN DOWN’S SYNDROME?
Although you may be having an amniocentesis to detect Down’s syndrome, the test may occasionally detect problems with the other chromosomes. If the results show anything abnormal you will be told what the abnormality is and how this will affect your baby.
WHEN IS AMNIOCENTESIS PERFORMED?
The test is most safely performed from 15 weeks of pregnancy onwards.
HOW IS AMNIOCENTESIS PERFORMED?
The test involves taking a small amount of the amniotic fluid (water) that surrounds the baby in the womb. This fluid contains cells from the baby that are tested in the laboratory.
Before the test is performed, an ultrasound scan is carried out to check your dates and the position of both the baby and the placenta (afterbirth). You will not need a full bladder for this scan.
The skin over the abdomen is cleaned and a fine needle is then passed into the womb. A sample of the fluid that surrounds the baby is removed and sent to the laboratory. The position of both the baby and the needle are monitored thoughtout the procedure by ultrasound.
IS AMNIOCENTESIS PAINFUL?
Most women say afterwards that the test is uncomfortable rather than painful and feels similar to period pain. Generally women say that the thought of it is worse than the actual test.
WHAT HAPPENS AFTER THE AMNIOCENTESIS TEST?
You will probably be at the hospital for about half an hour but the test itself only takes a few minutes.
If your blood group is Rhesus negative, you will need to be given an injection following the procedure to prevent the formation of antibodies in your blood, which may affect future pregnancies.
We encourage you to bring a companion with you for support during and after the test. It is a good idea to take things easy for a couple of days after the test, avoiding any heavy lifting or strenuous exercise.
The ‘period pain’ feeling may persist for 24-48 hours. This is not unusual and should settle with Paracetamol, which is safe to take in pregnancy. If you have excessive pain, are leaking any fluid / bleeding or develop a high temperature, please contact your local labour ward for advice.
WHEN DO YOU GET THE RESULTS?
The chromosome test involves growing the cells in the laboratory and this usually takes about 14 days.
If the chromosomes are normal, we will send you the result by post.
WHAT IF THE RESULTS ARE ABNORMAL?
If a chromosome problem is detected, your own Consultant will be contacted with the result. You would usually be contacted by telephone and given an opportunity to discuss the findings. You will be told what the abnormality is and how this could affect your baby. You will have the chance to discuss the results fully before making any decisions.
HIV INFECTION
We would encourage women who are HIV positive to discuss this with their specialist midwife or doctor to obtain further information before invasive testing as there is a risk that the HIV virus can be passed to the developing baby during the procedure.
OUTCOME OF PREGNANCY
Outcome information is very important to us as this enables us to audit and improve our service. Following your appointment with us you will be given an outcome form and an addressed envelope, which we would be very grateful if you would complete and return to us.
….AND FINALLY
If you have any questions about amniocentesis please telephone the Fetal Medicine Unit at the Rosie on 01223-216185. We can arrange for a Fetal Medicine midwife to talk to you if you wish.
We recognise that everyone will have his or her own particular questions and concerns to discuss. The midwife will usually be able to answer any questions you may have before you have the test.