With amniocentesis or amniocentesis (άμνίον of Greek amnion , Embryonalhülle and κέντησις kentēsis , stinging) is in medicine, carried out with a hollow needle puncture of the amniotic sac (amniotic cavity) of a pregnant woman for the investigation of the amniotic fluid contained fetal cells genetic or for the detection of biochemical damage designated. Colloquially one speaks of amniotic fluid puncture . If an amniocentesis is done, it is usually done in the second trimester of pregnancy.
Time of examination
Amniocenteses are usually performed between the 15th and 18th week of pregnancy. However, they are also possible from the 10th week (early amniocentesis), at which point there is an increased risk of injury to the unborn child and an increased risk of miscarriage . It was found that amniocentesis increased the miscarriage rate from 0.82% to 1.31%. This is why early amniocentesis is only carried out in particularly urgent cases or at the special request of the pregnant woman or the parents.
To prepare for the amniotic fluid collection, the doctor first determines the position of the child in the uterus by means of an ultrasound scan in order to find a suitable puncture site for amniotic fluid collection . At the selected point, a thin needle is inserted into the abdominal wall and further into the amniotic sac ( puncture ) under ultrasound control .
About 10 to 20 ml of amniotic fluid is removed, in which there are cells of the amnion (= the amniotic sac surrounding the child) and child cells. The amniotic fluid sample is then examined in a laboratory. There the cells that are in the sample are further cultivated and multiplied. These cells are shed cells from the child's skin, gastrointestinal tract and kidneys. The first results of the amniotic fluid test can be available after 24 to 48 hours using the FISH test , although long-term cultivation must be awaited for a comprehensive diagnosis. After the procedure, the pregnant woman should consistently take it easy for a day.
In June 2012 it was announced that scientists in Seattle had succeeded for the first time in deciphering the genome of a human embryo from the parents' blood and saliva without the need for an amniotic fluid test.
Duration of the investigation
The amniotic fluid collection usually takes 5 to 15 minutes. Most women feel the needle sticking into the abdominal wall in the same way as a normal injection when taking blood or similar punctures. As a rule, it is not associated with any particular pain, so that the injection site is usually not anesthetized.
This makes it possible to assess certain undesirable developments in the central nervous system (CNS) , as well as some hereditary diseases (e.g. Apert syndrome ) and some chromosomal peculiarities, including Down syndrome (trisomy 21), Patau syndrome (trisomy 13), Edwards Syndrome (trisomy 18), trisomy 8 and trisomy 9 can be diagnosed with almost 100 percent certainty.
However, not all congenital diseases and disabilities can be determined, for example trisomies (= tripling of genetic material) sometimes appear as a so-called "mosaic". This means that the respective chromosome is not present in triplicate in all cells of the child, but there are also cells with the usual set of chromosomes. It is therefore possible that a mosaic trisomy will not be detected in the chromosome examination.
If the pregnant woman wishes, a paternity test can also be carried out (for example after a rape) with the help of amniocentesis.
In addition, the examination of the amniotic fluid (at least from the second trimester of pregnancy) allows the determination of further parameters:
- The acidity of the amniotic fluid provides information on the oxygen supply to the unborn child.
- The amount of alpha-fetoprotein ( alpha-1-fetoprotein ) provides information on various neural tube defects with an accuracy of around 90% (see triple test ), whereby examinations with high-resolution ultrasound technology ( fine ultrasound , 3D ultrasound , 4D -Ultrasound ) must be performed.
From around the 30th week of pregnancy, amniocentesis can also be carried out to diagnose blood group incompatibilities between the pregnant woman and the unborn child, and in the event of an impending premature birth it is possible to assess the lung maturity of the unborn child through the examination .
In the case of first-time mothers over 35 years of age or late mothers over 40 years of age , the health insurance company pays for the amniocentesis, as this is a risk pregnancy from this age onwards .
Risks involved in the examination should be weighed up by the pregnant woman or the parents before they consent to an amniocentesis. The following events can occur during or after the procedure:
- Amniotic fluid loss
- Bleeding in the womb
- Injuries to the uterus
- Violations of the mother cake
- Injury to the unborn child from the needle (especially if the child moves a lot and / or unexpectedly)
- more frequent occurrence of malformations (increased risk of clubfoot)
- Uterine contractions (often noticeable as a kind of "pulling" in the abdomen, which in most cases subsides)
Due to the increased risk, invasive examinations are usually carried out if, in particular, the risk of miscarriage as a result of the procedure is lower than the statistically expected probability of the presence of a chromosomal feature or a hereditary disease .
After the procedure, the pregnant woman should consistently take it easy for a while, as it is in principle still possible for days after the procedure that, e.g. B. comes to amniotic fluid loss.
In a study from 2002, in which 1,006 amniocenteses were retrospectively evaluated, the miscarriage rate in an examination in the 16th or 17th week of pregnancy in women aged 20 to 34 years was 2.5%, an increase in the age group of Women aged 35 to 39 years to 3.4% up to 5.1% in women aged 40 and over. In addition to age, vaginal bleeding during pregnancy was an important risk factor that increased the incidence of miscarriages to 6.5% (= 2.4 times higher risk); Women with a spontaneous miscarriage in earlier stages of pregnancy or an abortion had an incidence of 8% (= 3-fold increased risk).
In another study, the complication rate (miscarriage, intrauterine fetal death ) within 14 days of an amniocentesis was 1.5% for training assistants and 0.6% for specialist doctors.
Antibody formation in case of rhesus incompatibility
Since puncturing the mother's uterus and the amniotic sac there is a fundamental risk of injuring the placenta , the umbilical cord or the child (see application risks ), in this case the child’s blood can get into the maternal amniotic fluid or the maternal when the needle is withdrawn Tissues become contaminated by blood components in children . If there is a blood group incompatibility ( Rhesus incompatibility ) to the Rhesus factor - antigen "D", i. H. between Rh-negative (Rh−, rh, genotype dd) mother and Rh-positive (Rh +, Rh, genotype Dd, dD, DD) child, antibody formation by the mother (called "anti-D") against the child's blood would be likely if it is through the above Process of introducing child's blood or its components ( erythrocytes or their components) into the maternal bloodstream . This process can also be initiated by other invasive interventions on the child or during pregnancy in the uterus (e.g. induced abortion or termination of pregnancy ; umbilical cord puncture ; chorionic villus sampling ). The risk increases depending on the extent of the invasiveness or the risk of injury and bleeding.
"Anti-D" is an irregular erythrocyte antibody that Rhesus negative people can produce if they are immunized by Rhesus positive erythrocytes . The drug ("anti-D prophylaxis", such as RHOPHYLAC from CSL Behring and RHESONATIV from Octapharma), which is usually administered prophylactically against this process and its consequences in children (see Rhesus incompatibility # pathogenesis ) is also called this.
- Heide Hohenstein: Disruptive factors in the processing of feelings during pregnancy: Social and ethical background to amniotic fluid puncture - interviews with those affected and discussion of their experiences. Verlag Waxmann, Berlin 1998, ISBN 3-89325-613-X .
- Prenatal Diagnostics Working Group
- Familienplanung.de - Amniocentesis : The information portal of the Federal Center for Health Education (BZgA)
- www.spektrum de: Amniocentese
- Amniotic fluid examinations: residual risk remains
- The word describes the process: gr. Ἀμνίον amníon , " amniotic sac" + κέντησις kéntēsis , "puncture". In German it should read * Amnio k entese, but the word penetrated through the Latin language, according to which Greek κ is written as c .
- Nicola Kuhrt: genetic test: researchers decipher the embryo genome from the parents' blood and saliva. on: Spiegel online. June 6, 2012.
- JO Kitzman, MW Snyder, M. Ventura, AP Lewis, R. Qiu, LE Simmons, HS Gammill, CE Rubens, DA Santillan, JC Murray, HK Tabor, MJ Bamshad, EE Eichler, J. Shendure: Noninvasive Whole-Genome Sequencing of a Human Fetus. In: Sci. Transl. Med. 4, 137, June 2012, p. 137ra76.
- NE Papantoniou, GJ Daskalakis, JG Tziotis, SJ Kitmirides, SA Mesogitis, AJ Antsaklis: Risk factors predisposing to fetal loss following a second trimester amniocentesis. In: BJOG - An International Journal of Obstetrics and Gynaecology . 108, 2001, pp. 1053-1056. doi: 10.1111 / j.1471-0528.2001.00246.x , PMID 11702837
- D. Bettelheim, B. Kolinek, A. Schaller, G. Bernaschek: On the complication rate in invasive, intrauterine interventions in a prenatal diagnostic department . In: Ultrasound in Med. 23 (2), 2002, pp. 119-122, doi: 10.1055 / s-2002-25191 , PMID 11961726 .