Amniocentesis is an optional part of prenatal care during pregnancy. This procedure is used to screen for developmental abnormalities and birth defects in the unborn baby.
Below you will find additional information as well as a selection of specialists who perform amniocentesis.
Background on Prenatal Diagnostics
There are various forms of prenatal diagnostics. The goal of all these procedures is to monitor the development of the fetus and screen for possible disorders. Some procedures assess various risks purely on a statistical basis, such as first-trimester screening. Others use tissue cells from the unborn child for testing (invasive diagnostics).
Amniocentesis, like chorionic villus sampling, is a form of invasive, optional prenatal diagnosis.
Invasive diagnostic tests provide reliable information about possible genetic disorders. They are particularly effective in detecting chromosomal abnormalities, such as Down syndrome.
During amniocentesis, amniotic fluid is extracted from the amniotic sac. The amniotic fluid contains cells of fetal origin. These can be tested for genetic disorders.
Amniocentesis uses fluid from the amniotic sac of the pregnant woman © Sora_Kobayashi | AdobeStock
When is amniocentesis performed?
Amniocentesis can be performed starting in the 16th week of pregnancy. If earlier testing is necessary during pregnancy, a chorionic villus sampling (CVS) is performed.
Amniocentesis is not part of routine prenatal care and is performed only at the express request of the parents. It is generally preceded by a prior test, such as first-trimester screening or cell-free DNA analysis, that has yielded an abnormal result. The test may also be advisable in cases of certain hereditary conditions in the family.
Before the procedure, the doctor must inform the parents about
- possible side effects of the procedure as well as
- the consequences of a diagnosis of a genetic disorder
in detail and in a way that is easy to understand. For the disorders that can be detected through amniocentesis, there is generally no causal treatment available yet. Therefore, parents who are told their child is likely to have a genetic disorder must decide whether they wish to continue the pregnancy.
Nevertheless, the diagnostic test can also be beneficial regardless of whether parents decide to continue the pregnancy or not. It gives parents who choose to have the child time to prepare and gather information. In some cases, this also makes it possible to create better conditions for the child’s optimal development. This is the case, for example, with hemophilia or rare metabolic disorders.
How is amniocentesis performed?
Before the amniocentesis, a thorough ultrasound examination is performed first. It is used to assess the fetal organs and the position of the placenta.
The amniocentesis is performed transabdominally, meaning through the abdominal wall. Under ultrasound guidance, the doctor inserts a thin hollow needle into the amniotic cavity and withdraws about 15 ml of amniotic fluid. The procedure takes only about a minute and is barely painful.
The extracted amniotic fluid is cultured in the laboratory (the cells are further multiplied) and examined. The results are available after about 14 days. If necessary, a rapid test can be performed beforehand to screen for
- to screen for trisomies 21, 18, and 13 (Down syndrome, Edwards syndrome, Patau syndrome) and
- abnormalities in the number of sex chromosomes
can be ruled out or diagnosed. However, these are generally additional services subject to a fee.
After about 14 days, the cell culture can also be used for molecular biological DNA analysis.
Important to know: In practice, this test by no means covers the entire spectrum of possible genetic abnormalities. Doctors look only for specific genetic changes for which there are reasonable grounds for suspicion. These primarily include fetal malformations and a family history of such conditions.
How reliable are the results of amniocentesis?
The results of amniocentesis are generally very reliable. This is particularly true for common chromosomal abnormalities such as Down syndrome.
In very rare cases, the fetus may have cells with different genetic makeup (the technical term for this is mosaicism). In such cases, the next steps must be discussed on a case-by-case basis.
What are the risks of amniocentesis?
A slightly increased risk of miscarriage is the greatest risk associated with any invasive diagnostic procedure. This risk has been significantly reduced in recent years. Recent analyses of large datasets have shown that the additional risk of miscarriage due to amniocentesis is approximately 0.1 percent. Of course, the examiner’s experience is of great importance here.
For Rh-negative mothers, there is a risk of Rh incompatibility (if the baby is Rh-positive). In such a case, the mother produces antibodies against the fetus as soon as fetal blood enters her bloodstream, which can occur when the biopsy needle is withdrawn.
Rhesus prophylaxis (a type of vaccination) administered immediately after amniocentesis prevents this immune reaction.
