Amniocentesis also referred as amniotic fluid test, it is a minimally invasive test which is used in prenatal analysis of chromosomal abnormalities in which little amount of amniotic fluid which includes fetal tissues, is sampled from the amniotic sac near growing fetus and fetal DNA is observed for inherent abnormalities. The main reason to have an amnio is to verify whether a child has positive genetic disorder or a chromosomal irregularity such as Down syndrome. Amniocentesis (Chorionic Villus Sampling) can analyze this problem in the womb. Amniocentesis is generally done when woman is between 14 – 16 weeks of pregnant. Women who prefer this test are mainly at a high risk for chromosomal and genetic problems.
Genetic diagnosis
Amniocentesis is used for identification of chromosomal and fetal issues such as:
- Down syndrome
- Trisomy 18
- Trisomy 13
- Fragile X
- Rare, innate metabolic disorders
- Neural tube deficiency by alpha-fetoprotein levels.
Procedure:
Firstly, local anesthetic is given to the woman in order to reduce the pain felt during the inclusion of the needle used to extract the fluid. After the local anesthetic is in effect, a needle is usually inserted into the woman’s abdominal wall, then the wall of the uterus and lastly into the amniotic sac. With the assistance of ultrasound guidance a physician punctures the sac in a part away from fetus and extracts something like 20ml of amniotic fluid. If it is used for prenatal genetic diagnosis, fetal cells are divided from the extracted sample. The cells are developed in a culture medium, then fixed and stained. Under a microscope the chromosomes are examined for abnormalities. The common abnormality identifies Down syndrome, Turner syndrome (monosomy X) and Edwards’s syndrome (trisomy 18). In regards to the fetus, the puncture seals and the amniotic sac replenishes the liquid over the next 24–48 hours.
However thanks to the advent of tests such as Double Screen/Triple screen and NIPT such as Maternity 21, Amniocentesis is an outdated procedure.
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