Amniocentesis: yes or no?

The amniotic fluid test is a diagnostic test of your unborn child for hereditary diseases, malformations and chromosomal abnormalities. For this purpose, the amniotic sac is punctured and amniotic fluid is removed. The fetal cells contained in the amniotic fluid are examined. The results provide 98 percent reliable knowledge for many diseases. Nevertheless, amniotic fluid testing is not recommended for every pregnant woman, as it also carries the risk of a miscarriage or other complications.

When is an amniocentesis performed?

Amniocentesis is the oldest invasive procedure in prenatal diagnosis . It was used more than 100 years ago to treat excessive amounts of amniotic fluid. Today, amniocentesis is a standard method to determine the fetal chromosome set. The optimal time for an amniotic fluid test is from the 15th week of pregnancy . Theoretically, amniocentesis would be possible from the eleventh week of pregnancy , but due to the increased risk of premature birth in this early phase of pregnancy, it is only very rarely performed, for example to enable earlier intervention and to give the expectant parents more time.

What diseases can you identify?

An amniotic fluid test can, for example, show the following clinical pictures:

  • hereditary diseases
  • Malformations (heart defects, cleft lip and palate, etc.)
  • Chromosomal abnormalities such as Down syndrome (trisonomy 21) and Edwards syndrome (trisonomy 18)
  • Damage to the nerve tracts such as spina bifida
  • Causes of a previous unexplained miscarriage
  • Infections, such as toxoplasmosis , cytomegaly , rubella, and bacterial infections

When do doctors recommend an amniotic fluid test?

  • The results of the first trimester screening are striking.
  • The pregnant woman already has a child with a malformation, hereditary disease or chromosomal abnormality, or there were abnormalities in a previous pregnancy.
  • The results of the antibody screening test indicate Rhesus factor intolerance. Here, an amniotic fluid test can help diagnose jaundice or anemia in the child.

In order to come to a recommendation, the gynecologist will weigh the existing indications of chromosomal abnormalities, malformations or hereditary diseases with the risks of the amniotic fluid test. In a consultation, he will discuss these considerations with the pregnant woman and support her in the decision.

Should I opt for amniocentesis?

Pregnant women should ask themselves the following questions before making this decision:

  • Are you willing to take the risk of this invasive procedure (see below)?
  • Do you want to be prepared for a possible disability before the birth?
  • How do you deal with the waiting time until the results are there?
  • How would you deal with a conspicuous finding?
  • Does this finding play a role in continuing the pregnancy?

What happens during the amniocentesis?

The amniotic fluid test is not very painful or strenuous for you. The whole examination only takes about 15 minutes.

  • First, the position of the child in the uterus is determined by ultrasound. In this way, the ideal puncture site can be found that does not injure the baby. A spot where most of the amniotic fluid has accumulated is preferred. The doctor tries to stay as far away from the baby and the sensitive areas of the placenta as possible.
  • Before the procedure, the pregnant woman can opt for a local anaesthetic, but this is not absolutely necessary.
  • The pregnant woman is then pricked with a needle through the abdominal wall into the uterus. That sounds bad at first, but is usually no more painful than drawing blood. About 20 to 25 milliliters of amniotic fluid are removed from the amniotic sac with the needle. The amniotic fluid contains the baby’s skin cells and cells from the intestines and kidneys.
  • Rhesus-negative women are given anti-immunoglobin as a precaution.
  • After the amniotic fluid test, a pregnant woman should rest for a few days. You should avoid exercise, sex, and heavy lifting for at least 48 hours. It is best to get time off work as well.
  • The so-called “FISH method” means that the mother does not remain in the dark for too long: the first results for the determination of chromosomes 13, 18 and 21 as well as sex chromosomes X and Y are available after 8 to 24 hours. In 99.6 percent of the cases, the rapid result agrees with the long-term culture. However, it will be two to three weeks before these results are available.

What are the fetal cells tested for in the lab?

  • The FISH test is carried out in the laboratory first. This test only checks the number of chromosomes, but says nothing about the composition of the chromosomes. The advantage is that the result of the FISH test is available after just two days.
  • After the FISH test, a chromosome analysis is performed. It shows whether all the chromosomes of the unborn child are present and formed correctly. With this analysis, certain malformations of the central nervous system as well as some hereditary diseases and chromosomal peculiarities can be identified. Since the cells from the amniotic fluid first have to be multiplied in the laboratory for this analysis, it unfortunately takes about three weeks before the results are available.
  • A DNA analysis can provide information about possible hereditary metabolic and muscle diseases in the unborn child. A neural tube defect, a so-called open spine, can also be detected by the amniotic fluid test. For this purpose, the proteins contained in the amniotic fluid are examined.
  • From the 30th week of pregnancy , the cells contained in the amniotic fluid can also be used to diagnose blood group or Rhesus factor intolerance.
  • And if there is a risk of premature birth, the amniotic fluid test can be used to assess the maturity of your unborn child’s lungs.

How reliable are the results?

Since the amniotic fluid test is a diagnostic test of the actual child’s tissue and not a screening test that only assesses a probability, it is 98 percent reliable in determining many clinical pictures. However, this only applies to the clinical pictures that are specifically tested for. Many other diseases are not tested without the existence of a specific indication. An inconspicuous finding does not guarantee that the child is one hundred percent healthy.

Alternatives to amniocentesis

In addition to the amniotic fluid test, other diagnostic tests are also available. Which one the doctor recommends depends on the week of pregnancy and the specific question (age, history or abnormalities in previous tests). Instead of the amniotic fluid test, in which the amniotic sac is punctured, a chorionic villus biopsy (puncture of the placenta) or an umbilical cord puncture can also be performed. Hasn’t been a triple test yetcarried out, this blood test can also be preferred to an invasive method such as the amniotic fluid test. In addition, a new blood test will be approved in Germany in 2012, which in many cases could replace amniocentesis in the long term. Find out more about the ” New blood test for the early detection of Down syndrome “.

Risks of amniocentesis

Because amniocentesis is an invasive procedure, it carries certain risks.

  • The sting can cause bleeding at the puncture site.
  • Infection is also possible, but fortunately extremely rare.
  • The miscarriage rate in late or routine amniocentesis is relatively low, at about 0.2 to 1 percent.
  • In the case of a puncture under ultrasound control, it is extremely rare for the child to be injured. In order to reduce the risk even further, punctures are made in the area of ​​the child’s legs or back if possible.
  • If membranes rupture after amniocentesis, immediate check-up in the clinic is important. But if the mother consistently keeps to bed rest and rest for a few days, there is usually a quick all-clear: the amniotic sac usually closes again by itself and the pregnancy continues as normal.

Consequences of a conspicuous finding

Many couples ask themselves before deciding for or against the amniotic fluid test what role an abnormal finding would play for them. Do you keep the baby? Or would an abortion be an option? You can find more information on how to deal with this finding and tips on where to find help in our article “ Termination of pregnancy with a finding of “Down Syndrome”? “.

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