Amniocentesis

What is amniocentesis?

Katarzyna Mikołajczyk, Doctor of Medicine

Amniocentesis is a test that involves puncturing the amniotic cavity where the foetus develops under ultrasound and collecting amniotic fluid for cytogenetic/molecular examination. It is an invasive prenatal test that is used to determine when there is an increased risk of foetal genetic abnormalities (chromosome aberrations or gene mutations) detected by non-invasive tests or on the basis of family history. It involves the examination of the chromosomes of the amniocytes, i.e. the exfoliated cells of the foetus present in the amniotic fluid, e.g. from the surface of the skin, digestive, respiratory or urinary systems. The examination, however, has its limitations. Cytogenetic examination evaluates the number of chromosomes in the foetus (the so-called chromosome aberrations) and allows the following diseases to be detected: Syndromes of Down, Edward, Patau, Turner, Klinefelter as well as triploidies.  Targeted molecular testing examines the material of the foetus for a specific genetic disease – e.g. cystic fibrosis, muscular dystrophy.  In summary, there are no genetic tests that can detect all possible genetic defects.

The waiting time for the result of a cytogenetic test from standard cell culture takes about 21 days, it is possible to additionally speed up the test with the QF PCR genetic probe method (for an additional fee) – then the result is expected to be up to 7 days.

How is the test performed?

The test is performed in the supine position. After disinfecting the skin with a sterile puncture set, under ultrasound control, the doctor punctures the uterus through the abdominal wall and takes amniotic fluid for examination (about 10-15 ml). The procedure is performed with a very thin needle (22G) – similarly to anaesthesia for labour, it is painless and does not require anaesthesia. In rare situations, several punctures may be necessary when amniotic fluid is not obtained from the first puncture. It is equally rare that a result is not obtained – this usually occurs when there is too little amniotic fluid or it is contaminated with blood.

Are there any contraindications?

The patient should be healthy (it is not advisable to be tested during an infection). Symptoms of threatening miscarriage (bleeding from the genital tract, lower abdominal pain) are contraindications. Also, bleeding from the genital tract up to 2 weeks before the examination is a contraindication, because in such a situation it is very likely that the amniotic fluid may be contaminated with the mother’s blood and it will not be possible to isolate the foetal cells.

Amniocentesis is performed after the 15th week of pregnancy because of the lower risk of complications after the procedure and a sufficiently large amount of amniotic fluid.

Any use of anticoagulants – heparin, Acard – should be consulted before the examination.

Are there any complications?

As with any procedure, amniocentesis carries a risk of complications. Statistically, the risk is around 0.5%.  The most serious complications are: infection, bleeding from the genital tract, discharge of amniotic fluid, miscarriage. For this reason, it is performed only in justified cases, when the risk of the defect in the foetus is greater than the risk of complications.

Are there any other invasive genetic testing methods?

Other methods of similar sensitivity include:

• chorionic villus biopsy – performed between 10 and 14 weeks
• cordocentesis – performed after the 20th week of pregnancy, consisting in direct foetal blood sampling from the umbilical cord vein.

Who refers for invasive testing?

Amniocentesis is performed on the basis of a referral from the doctor providing prenatal care. At the same time, it is necessary to provide a consultation with a geneticist who qualifies you for the above-mentioned examination (i.e. determines whether invasive tests are justified).

What if I have a negative blood type?

It is essential to provide an up-to-date anti-RhD antibody test. Due to the risk of maternal-foetal leakage during the examination, all patients after amniocentesis should receive 150 g of anti-Rh D immunoglobulin.

How to prepare for the test?

Before amniocentesis, it is necessary to consult the doctor performing the examination in order to assess the completeness of the documentation and discuss the details of the examination.

Fasting on the day of the examination is not required.

The examination is performed on an outpatient basis, and after a short observation the patient goes home with recommendations for further treatment (recommended conduct, symptoms of concern, setting a date for a follow-up examination, date for receiving the result).

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