What is an amniocentesis?
A specimen of amniotic fluid is obtained by placing a needle through the abdominal wall into the womb’s cavity.
The fluid and cells in the amniotic fluid originate from the baby, and can be used to diagnose specific conditions of the baby.
Why would an amniocentesis be done?
An amniocentesis is usually done to confirm or exclude possible abnormalities of the fetus (unborn baby), a so-called genetic amniocentesis.
An amniocentesis can also be done to evaluate the chemical composition of the amniotic fluid, for example to determine lung maturity or to assess possible blood group incompatibility. This information concerns genetic amniocentesis.
What are the reasons for a genetic amniocentesis?
As mentioned, a genetic amniocentesis is done to confirm or exclude possible abnormalities of the fetus (unborn baby). It is most commonly done because of an abnormal screening examination (first trimester ultrasound and blood test), or because of abnormal findings found at the structural ultrasound examination. Other reasons include advanced maternal age (35 years or older at the time of delivery) or a known genetic abnormality in the family.
Who decides whether a genetic amniocentesis is done or not?
Your doctor or genetic counsellor will explain to you why an amniocentesis is offered. It remains your own choice whether you would like to have an amniocentesis or not.
When is an amniocentesis done?
Generally, an amniocentesis is done between 16 and 20 weeks of gestation. The earlier it is done, the sooner the result is available, but the chances for complications are higher if it is done earlier.
Where is an amniocentesis done?
The amniocentesis is done in the consulting rooms, where an ultrasound is present.
How is an amniocentesis done?
With an ultrasound examination, the position of the placenta (afterbirth) and baby is determined in the womb and the best place for the amniocentesis is chosen. The doctor will be assisted by a nursing sister A thin needle is placed through the abdominal wall into the amniotic cavity and a sample is taken. Local anaesthetic is not used. The needle is removed, and the baby’s heart action is shown to you by ultrasound. The procedure itself lasts about one minute. If your blood group is rhesus negative, and the baby’s father is rhesus positive, you will receive an injection to prevent antibodies developing against the rhesus blood group.
What can go wrong with an amniocentesis?
During the amniocentesis
The placenta or umbilical cord can be accidentally punctured. This produces blood-tinged amniotic fluid, and can make the interpretation of the chromosomes more difficult. (Especially if it is a female fetus, it can be difficult to distinguish between cells from the baby’s or the mother’s blood.) Usually the bleeding stops quickly, and it is then not dangerous.
The baby could be injured with the needle. The chance of this happening is decreased by watching the needle continuously by ultrasound, and by placing the tip of the needle close to the back wall of the womb. (If the baby should kick or move against the needle, it would hit the side and not the sharp tip of the needle.)
Sometimes, no amniotic fluid is obtained. This should happen rarely, but could mean that a second insertion of the needle is necessary.
After the amniocentesis
Amniotic fluid could leak out. This happens approximately once in 50 amniocentesis. If this should happen, you would notice slight watery vaginal discharge within a few days after the amniocentesis. Usually, the leak seals off after a week’s bed rest.
A miscarriage could occur. Symptoms of this include a cramping abdominal pain, worse than menstrual pains, as well as vaginal bleeding. This happens approximately once in every 300 amniocentesis. If you notice any of these symptoms, please contact your doctor immediately.
An infection could develop in the womb. Symptoms of this are fever, cold shakes, a constant pain over the womb, and sometimes an offensive vaginal discharge. If you notice any of these symptoms, please contact your doctor immediately.
Other rare complications, include the development of club feet (approximately once in 200 amniocentesis if the amniocentesis was done before 13 weeks), or respiratory problems of the baby after birth (especially if there was a prolonged amniotic fluid leak).
If you are HIV positive, there is an increased chance that HIV can be passed on to your baby if you have an amniocentesis.
When will the results be available?
- The result of the alpha feto protein, which is a test for spina bifida, should be available the following day.
- The provisional result of the chromosome analysis, which tests whether the baby has Down syndrome or other major chromosomal problems, should be available within three days.
- The results for rare conditions can take longer, around three weeks.
In both cases, we will contact you by telephone as soon as the result is available. A copy of the result is also forwarded immediately to your gynaecologist.
What are the alternatives to amniocentesis?
Screening tests such as an ultrasound examination (preferably between 11 and 13 weeks of gestation) and /or a blood test can give you a accurate estimate of your risk of having a baby with Down syndrome or other chromosomal abnormalities. If the risk is low, according to one or both of these tests, you might decide against an amniocentesis. Invasive tests (e.g. amniocentesis, cordocentesis or chorionic villus biopsy) is the only definite way currently available to exclude a chromosomal abnormality.
Non-invasive prenatal tests are currently under development internationally. This allows the DNA of the baby to be extracted from a blood sample of the mother.
Other invasive tests include cordocentesis and chorionic villus sampling.
Chorionic villus sampling (CVS) involves obtaining cells from the placenta, also by means of a needle aspiration through the abdominal wall of the mother. The risk of causing a miscarriage is probably similar to that of an amniocentesis (i.e. 1/300). Because the natural risk of miscarriage is higher at 10 – 12 weeks (when a CVS is typically done) than at 16 – 18 weeks (when an amniocentesis is typically done), there would be in total more miscarriages after CVS than after amniocentesis. A disadvantage of CVS is that a chromosomal abnormality could be found in the chorionic villi (originating from the placenta), which do not occur in the baby itself. CVS also does not give any indication of the baby’s risk of a spina bifida. The main advantage of CVS is that it is done much earlier. If a serious abnormality of the baby is found, a pregnancy termination would be much earlier and less traumatic.
Cordocentesis entails obtaining a blood specimen from the baby’s umbilical cord. It is usually only done after 20 weeks of gestation. There is approximately a 1% risk of miscarriage, but it has the advantage that a full result is available within a few days. It is usually done where a physical anomaly of the baby is found on ultrasound, or where there has been a delay in doing an amniocentesis.
Which results can I expect from the amniocentesis?
- The alpha feto protein value will, in conjunction with the ultrasound examination, give an idea of the baby’s risk of a spina bifida.
- The chromosome results should exclude or confirm the possibility of Down syndrome and other chromosomal abnormalities.
- It also indicates the baby’s gender. (Please indicate whether you would like to know this!)
- Rarely, the following could happen:
- A so-called chromosomal “mosaic” could be found. This means that some cells are normal, and others abnormal. It sometimes reflects the baby’s chromosomal make-up, but can also be due an effect of the cell culture. If a mosaic is found, it could be necessary to repeat the amniocentesis, or do a cordocentesis.
- Chromosomal abnormalities of uncertain importance, could be found. This includes findings such as:
- A translocation, where part of one chromosome is found in another chromosome. This might have implications for the baby once he/she has grown up, and has children of his/her own.
- Fractured chromosomes, where the chromosome breaks up in the cell culture. This might have health implications for the baby as an adult.
- Extra X-chromosomes. This might have implications for the baby once he/she has grown up, and has children of his/her own.
- The baby’s gender as seen on ultrasound might differ from the gender according to the amniocentesis. This might mean that the ultrasound is wrong, that an error has slipped in with the reporting of the results of the amniocentesis, or that a real difference exists between the baby’s genetic and physical gender. It is important to distinguish this difference before the birth!
Which precautions should I take before the amniocentesis?
- A full bladder is unnecessary for the ultrasound. An empty bladder is less uncomfortable!
- Bring someone along for moral support. It is possible to drive home by yourself, but still better if some else does the driving!
- Let us know if you have any bleeding tendency, or if you are using any medication (including low-dose aspirin or arnica).
- Arrange to have the rest of the day off work. (Please let us know if we should send you a note in this regard.)
- Make sure whether your medical aid will refund the amniocentesis – both the amniocentesis itself, and the analyses in the biochemical and cytogenetical laboratories. Please note that you will receive two separate accounts for the amniocentesis: one by ourselves for the procedure, and one by the laboratory for the alpha feto protein, cell culture and karyotyping. The laboratory fee will double for twins, triple for triplets etc.
- If you are HIV positive, there is an increased risk of transfer of HIV to the baby with an amniocentesis. If you are HIV positive, or would like to be tested for HIV before the amniocentesis, please let us know beforehand.
Which precautions should I take after the amniocentesis?
- Take the rest of the day off work, and rest at home. It is not necessary to stay in bed, but do not do any physically strenuous work or exercises.
- Do not pick up any heavy objects in the next two to three days. (Including a toddler!)
- Contact us or your gynaecologist if any of the following should develop:
- Stomach pains or cramps, worse than with a menstrual period, and which do not improve by using analgaesics. one or two tablets of paracetamol, e.g. Panado® or Dolorol®
- Vaginal bleeding
- Watery vaginal discharge
- Fever or rigors
- Offensive vaginal discharge