What is amniocentesis?

Amniocentesis is an invasive procedure in which a gynaecologist inserts a needle through the pregnant woman’s abdomen into the gestational sac to take a small sample of amniotic fluid. It contains the fetus’ cells, and those, in turn, contain its genetic material. The laboratory analyses this genetic material to identify potential chromosomal defects and neural tube damage.

Amniocentesis is most commonly performed between weeks 16 and 18 of pregnancy

Although the amniotic fluid is already present earlier, we have to wait for the amnion to fuse with the outer chorion. This usually happens in week 15 of pregnancy. Therefore, amniocentesis is performed from the 15th week of pregnancy onwards, most often until weeks 18 or 20. In the second trimester of pregnancy, this procedure can detect fetal chromosomal abnormalities and mutations in genes.

Doctors sometimes recommend amniocentesis even later, if the gestational sac leaks and they want to determine whether the uterus may be infected and needs to be treated. Amniocentesis can also help identify anaemia in infants whose mothers are RhD negative and might need a blood transfusion. In some cases, doctors decide for amniocentesis just before the scheduled date of delivery, as the procedure can help assess the maturity of the child’s lungs and predict whether he can breathe on his own.

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The risk of chromosomal defects increases with age

Although amniocentesis is performed for a variety of reasons, the main is an increased risk of a chromosomal defect. This risk varies in each pregnant woman and generally increases with age, especially in pregnant women over the age of 37. From the age of 30, the risk of having a child with Down syndrome triples every three years.

Risk of Down syndrome in live births (%)

The results are 99.9% reliable

Amniocentesis’ advantage is its extremely high predictive accuracy. It is 99.9% accurate in determining whether the fetus has chromosomal abnormalities, neural tube defects, or genetic defects. Unfortunately, it cannot predict the extent of these defects. Ultrasound and measurement of alpha-fetoprotein levels can help assess fetal defects.

Is amniocentesis dangerous for my child and me?

It is a usually safe, often urgent procedure. But as all invasive procedures during pregnancy, it poses certain risks. Because the doctor enters the womb with a needle, amniocentesis can trigger miscarriage and loss of the fetus. The chance of such a complication is, on average, 1-2 per cent.

Because the method is invasive and the needle comes near the infant, in rare cases it may damage both the fetus and the mother. Infection and other complications may also occur, but the likelihood is extremely low.

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Should all pregnant women undergo amniocentesis?

Definitely not. The high risk of Down syndrome is first assessed by gynaecologists using conventional screening methods such as nuchal screening, double and quadruple marker testing, or non-invasive prenatal screening test or NIPT by GenePlanet.

Amniocentesis is precise, but because of the undesirable effects of invasive methods, doctors recommend that pregnant women with increased risk of chromosomal defects of the fetus should first do a non-invasive risk assessment methods. Only later, with unfavourable results, should they resort to invasive procedures such as amniocentesis.

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Diagnostic procedure

Week
Risk of miscarriage

Amniocentesis

14-16

1-2%

Chorionic villus sampling (CVS)

10-12

1-2%

Percutaneous umbilical cord blood sampling

24-34

HIGH RISK

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