Amniocentesis is an antenatal examination that is performed like a chorionic villus biopsy to identify, among other things, chromosomal abnormalities in unborn children. Amniotic fluid is taken from the mother between the 14th and 18th weeks of pregnancy. The foetal cells present in this are then examined over a two-week period. Amniocentesis is generally harmless and the risk of it causing a miscarriage, compared to a chorionic villus biopsy, is similarly just 1%.
Although amniocentesis can provide valuable information about the health of the unborn baby, it is important to be aware of the risk of this antenatal examination and to be prepared for the results.
Why is it carried out?
Amniocentesis can be carried out for various reasons:
Genetic examinations
Genetic amniocentesis is carried out when indicated: A sample of the amniotic fluid is examined for certain illnesses such as Down’s syndrome (trisomy 21) or Apert syndrome.
Examination of the foetal lungs
When examining the maturity of the foetal lungs, a sample of amniotic fluid is taken and examined to see whether the baby’s lungs are mature enough for the birth.
Diagnosis of a foetal infection
Amniocentesis is sometimes carried out to examine the baby for an infection or other illness. The procedure can also be carried out to determine the severity of anaemia in babies with Rhesus sensitisation - a rare condition in which the mother’s immune system produces antibodies against a certain protein on the surface of the baby’s blood cells.
Treatment
If too much amniotic fluid accumulates during the pregnancy (polyhydramnios), amniocentesis can be carried out to drain excess amniotic fluid from the uterus.
Paternity tests
A DNA test can be carried out via amniocentesis. The DNA of the foetus is obtained and compared with the DNA of the potential father.
Possible complications during or after the examination
Leaking amniotic fluid
In rare cases, amniotic fluid leaks out of the vagina following amniocentesis. However, in most cases, the loss of fluid is low and stops within a week, so the pregnancy to likely to continue as normal.
Miscarriage
Amniocentesis in the second trimester poses a low risk of miscarriage - around 0.1 to 0.3 per cent. Research findings indicate that the risk of a miscarriage is greater when amniocentesis is carried out before the 15th week of pregnancy.
Injury due to the needle
The baby may move one of their arms or legs into the path of the needle during amniocentesis. However, severe needle injuries are rare.
Rhesus sensitisation
In rare cases, blood cells from the baby can enter the mother’s bloodstream during amniocentesis. If you have Rhesus-negative blood and have not developed any antibodies against Rhesus-positive blood, you will be given an injection of a blood product called Rhesus immunoglobulin after the examination. This prevents your body from producing Rh antibodies, which can pass through the placenta and damage your baby’s red blood cells. A blood test can identify whether you have begun to produce antibodies.
Infection
In very rare cases, amniocentesis can trigger a uterine infection.
Transmission of an infection
If you have an infection - such as hepatitis C, toxoplasmosis or HIV/AIDS - this infection can be passed on to your baby during amniocentesis.
Bear in mind that genetic amniocentesis is usually offered when the test results could have a considerable influence on the treatment for your pregnancy. The decision as to whether genetic amniocentesis is carried out ultimately lies with the mother. The healthcare professional or genetic counsellor can help to weigh up all of the factors.
What can be expected during the examination?
Amniocentesis is normally carried out in an outpatient, obstetric facility.
During the procedure
First of all, the doctor will determine the precise position of the baby in the uterus with the aid of ultrasound. The patient lies on her back on an examination table and uncovers her abdomen. The doctor will apply a gel to the patient’s abdomen and then use a small device, called an ultrasound probe, to show the baby’s position on a monitor.
The doctor then cleans the abdomen with an antiseptic. Local anaesthetic is not generally used. Most women report that they only feel slightly uncomfortable during the procedure.
Under ultrasound guidance, the doctor inserts a thin hollow needle through the abdominal wall into the uterus. A small amount of amniotic fluid is drawn into a syringe and the needle is removed. The amount of amniotic fluid taken depends on how many weeks you are into the pregnancy.
The mother should remain as still as possible while the needle is inserted and the amniotic fluid is removed. The patient may feel a pricking sensation when the needle penetrates the skin, and cramps may be felt when the needle penetrates the uterus.
After the procedure
Following amniocentesis, your doctor will continue to monitor the baby’s heart rate with the ultrasound device. The patient may feel cramps or minor discomfort in the pelvic region after amniocentesis.
A normal level of activity can be resumed after the examination. However, strenuous physical or sexual activities should be avoided for one or two days.
In the meantime, the sample of amniotic fluid is examined in a laboratory. Some results are already available after a few days. Other results can take up to four weeks.
The results
The test results for genetic amniocentesis can reliably rule out or diagnose various genetic conditions, such as Down’s syndrome (trisomy 21). However, amniocentesis cannot identify all genetic conditions and birth defects.
The test results can also reliably indicate the maturity of the baby’s lungs. If the mother needs to deliver the baby prematurely, this information can offer reassurance that the baby is ready for the birth.
If amniocentesis shows that the baby has a chromosomal or genetic abnormality that cannot be treated, parents may face tough decisions - for instance, whether the pregnancy should be continued. The support of the medical team and relatives is all the more important during this time.