Amniocentesis

Amniocentesis is a common prenatal test in which a small sample of the amniotic fluid surrounding the fetus is removed for testing.

Features

Amniocentesis is often used during the second trimester of pregnancy (usually 15 to 18 weeks after a woman's last menstrual period) to diagnose or, much more often, rule out certain chromosomal defects and genetic. This is a routine test and is done only if the doctor suspects an abnormality that cannot be detected by other tests, which would seriously interfere with the pregnancy. The detached cells floating in the fluid are used to obtain an accurate chromosome count and to detect any abnormal chromosome structures. It is also possible to determine the amount of oxygen and carbon dioxide present in the fluid and find out if the fetus is getting enough oxygen or is at risk. In cases of Rh incompatibility, the bilirubin content in the fluid will indicate whether the baby requires an intrauterine transfusion.

Amniocentesis is done to determine if the baby has:

• Some aneuploidy (change in the number of chromosomes) such as Down's syndrome (Pair 21 trisomnia).
• Some disease that affects metabolic, neurological, etc. functions.

Your baby's sex can be determined by studying some skin cells, which can help find out if you've inherited any sex-related disorders. However, the purpose of this procedure is not to know the sex of the fetus and after its completion there is a certain risk of abortion (due to bleeding or infection) so if there is no medical indication it is not recommended.

Amniocentesis and stem cells

Recently it was shown that amniotic fluid contains differentiated and undifferentiated embryonic and extraembryonic tissue cells derived from ectoderm, mesoderm, and endoderm. The typology and characteristics of amniotic fluid cells vary depending on the time of infusion. gestation and depending on the existence of possible fetal pathologies. Some studies (for example by Paolo De Coppi, Antony Atala, Giuseppe Simoni) demonstrate the presence of mesenchymal fetal stem cells with differentiating potential towards cellular elements derived from three embryonic leaves. They are cells that expand easily in culture, maintain genetic stability and can be induced to differentiate... and therefore represent a new source of cells that could have multiple applications in tissue engineering and cell therapy, especially all for the treatment of congenital anomalies in the perinatal period.

Stem cells from amniotic fluid present no ethical controversy and it is possible to recover them if they are kept in banks for one's own use.

Risks of Amniocentesis

Performed by an expert and with the help of an ultrasound scanner, to determine the position of the placenta and the baby, the risk of miscarriage is lower than with the transvaginal chorionic biopsy test (2%), but it is the same as transabdominal chorionic biopsy (0.8%).^{[citation needed]}

Results

Results from amniocentesis take about three weeks. Apart from this, there is a genetic test, called FISH (fluorescent in situ hybridization), with which, in 48 hours, we can know if the fetus has alterations in the pairs of chromosomes, 21, 18, 13 or alterations in the X and e sex chromosomes. And, at the same time that it informs us of the fetal sex.

The test can focus on certain chromosomal regions, not giving us information on the rest.

Another common problem in amniocentesis is the presence of mosaicism in the collected cells. It is very common for cases of mosaicism to be detected but they will not always be correct. In fact, most of the mosaicisms found in these tests do not correspond to the true karyotype of the fetus. There are actually more cases of mosaicism in extraembryonic tissues than in embryonic tissues. Normally a perfect match is sought between cells of the placenta and the fetus.

Procedure

After an examination with a scanner, to determine the position of the fetus and placenta, a long needle is inserted into the uterus, without local anesthetic. Approximately 14 cm³ of fluid is removed from the amniotic sac, which is centrifuged to separate the detached cells of the fetus from the rest of the fluid. These are cultivated for a period of between 2½ and 5 weeks.

Indications for amniocentesis

• Female over 35 years of age, from which the risk of chromosomal abnormalities increases considerably.
• Family history of chromosomal alteration.
• Diagnosis with a view to termination of pregnancy.