AIPMT-NEET Biology Aspirants, read out the next AIPMT-NEET Biology Study material/ Notes of Amniocentesis.

It is a prenatal diagnostic test, i.e. a test done during pregnancy to identify any chances of genetic disorder.

Amniocentesis is amnio- plus -centesis. Amnio means amnion- an innermost membrane enclosing the embryo. Amnion makes the cavity around the embryo called as amniotic cavity in which fluid is filled called as Amniotic fluid. Amniotic fluid acts as a shock-absorber for embryo, maintains proper temperature for fetus. –centesis means removal of amniotic fluid from amniotic cavity.

• Amniotic fluid contains fetal cells so it is used for testing the presence of any genetic disorder/chromosomal abnormalities like Down syndrome, Hemophilia, Tay-sachs disease, sickle cell anemia etc.
• This test is usually done in 14-18 weeks of gestation/pregnancy.
• This test can also reveal the sex of the baby.
• Amniocentesis leads to risk of spontaneous abortion by 0.5% after it is done, so it is performed only when there is any suspicion of genetic disorder.

How it is done:  Local anesthesia is given to the mother. A needle is inserted in the abdominal wall of mother to the amniotic cavity to take about 10-30 mL of amniotic fluid. Fluid contains fetal cells and some dissolved substances. This fluid is tested by microscopic and biochemical examination.

For testing of chromosomal disorder, fluid cells are cultured for 2-4 weeks to reveal missing, extra or abnormal chromosomes.

• High level of AFP (Alpha-fetoprotein) and acetylcholinesterase may indicate failure of development of nervous system as in case of spinal bifida or anencephaly (absence of cerebrum). AFP is a protein synthesized by liver of the fetus and passes into maternal blood circulation.

NOTE:  1)  Fetal Ultrasonography (commonly called as ultrasound), Chronic- villi sampling (CVS) are other prenatal diagnostic tests done to access fetal well-being and genetic disorder. Ultrasound is done to check fetal growth, fetal age, its position, twins, etc.  CVS is done for genetic disorder and can be performed at 8-weeks of pregnancy and it is more riskier than amniocentesis.

While CVS and amniocentesis require penetration of needle or catheter into the embryonic structures, AFP test is non-invasive test as it requires mother’s blood for diagnosis. AFP test done for Down-syndrome, trisomy 18, neural-tube defects. This test is safe and less expensive than other tests.

2) Sex determination of fetus is banned in India due to female foeticide.