Pregnancy is a worrying time for some, but it is important to remember that most people have healthy babies. Some women however are more likely than average to have a child with a genetic problem, and these women may be offered a test in pregnancy. Various prenatal procedures are available, generally being performed between 10 and 20 weeks’ gestation. One of these tests is amniocentesis. The test is important factors that must be considered.
Amniocentesis is used most often to detect chromosome disorders, with Down Syndrome (previously called Mongolism) being the most common.
Amniocentesis can also pick up most cases of Spina Bifida (a disorder where the spine does not form properly). Most laboratories will routinely test for this, even if the amniocentesis is not for this particular reason.
Some other genetic orders can also be detected, but the laboratory must be informed that there is a history of another genetic problem in order for additional test to be carried out.
Of course, the final decision about the test is yours, but the following women may be offered amniocentesis:
Mother’s age and risk of having a Down Syndrome Baby:
|25 years – 1in 1250||38 years – 1 in 150|
|30 years – 1in 900||40 years – 1 in 90|
|35 years – 1 in 300||45 years – 1 in 25|
The test involves taking a sample of the amniotic fluid (‘water’) which surrounds the baby in the womb. This fluid contains cells from the baby and substances from the pregnancy, which can be tested in the laboratory.
Amniocentesis is an outpatient test, usually done at around 14 to 16 weeks of pregnancy (calculated from the first day of your last menstrual period). You do not have to be admitted to hospital or have a general anaesthetic.
An ultrasound scan is done first, to check the stage of the pregnancy and the position of the baby and the placenta (afterbirth). You will need a full bladder for this scan. The skin over the womb area is then cleaned with antiseptic solution, after which a fine needle is passed into the womb and a sample of the fluid that surrounds the baby is withdrawn with a syringe Then the sample is sent to the laboratory.
Most women say that the test is not a painful one, and feels no more painful than having a blood test or an injection. Generally, women agree that the thought of it is worse than the actual test!
The test may take up to 25 to 35 minutes in total (including the ultrasound scan). Afterwards, it is suggested that you go home and rest for the remainder of the day. It is also a good idea to take things easy for few days thereafter and avoid any heavy lifting or strenuous exercise. Sometimes women get a ‘tightening’ feeling in the womb afterwards, and/or feel a little sore the next day. This is not unusual, but if you are worried about anything do contact your doctor.
The chromosome test (mainly for Down Syndrome) involves ‘growing’ the cells in the laboratory, and the results for this usually take about 3-4 weeks. The Spina Bifida results are faster, and only take about 2 days. Your doctor will be sent the results. In the event of a problem being found, your doctor will be telephonically contacted and you will be offered the opportunity of discussing the findings with a genetic counsellor. Very occasionally, the cells do not grow well in the laboratory and the amniocentesis will have to be repeated in order to obtain a result. If this happens, your doctor will be contacted immediately and you will be requested to have the procedure repeated, please inform your doctor.
If the results are abnormal, this will be discussed with you and you will be told how the abnormality is expected to affect your baby. You and your partner can then consider whether or not you want to continue with the pregnancy and you will be given a chance to fully discuss the findings before making any final decisions. If you decide that you want to have the pregnancy terminated, this can usually be arranged fairly quickly and is legal under the South African Abortion and Sterilization Act.
Amniocentesis is a well-established and widely available method for prenatal diagnosis. However it is known that the test can sometimes cause a miscarriage. It is estimated that about 1 in every 150 women who have the test will miscarry as a result of the procedure. (The skill of the practioner will to a large extent determine the risk of miscarriage). Most of these miscarriages will occur within 2 weeks of having the test. Other than this, it is believed that in general, amniocentesis is NOT harmful to you or your baby.
The chromosome part of the amniocentesis is very accurate. The Spina Bifida test on the fluid is not quite accurate, but does pick up the great majority of pregnancies with an opening in the spinal column.
If you are having an amniocentesis for other genetic reasons, you should discuss the accuracy of the test, in your particular case with a genetic counsellor or the doctor in charge of the genetics laboratory.
It is not possible to write everything down here, and people may have their own particular questions and points they wish to discuss. Therefore, please ensure that your doctor or a genetic counsellor answers your questions before you decide whether you would like the test performed.