Category : 12th Class
Aim : It is a technique to determine :
(1) Sex of the developing baby.
(2) Genetically controlled congenital diseases.
(3) Metabolic disorders in foetus.
So amniocentesis is a pre-natal diagnostic technique.
Procedure : It involves following steps :
(1) Location of the foetus is determined by a technique called sonography (using high frequency ultrasound waves) to prevent accidental damage to the foetus.
(2) A fine hollow needle is passed through the abdominal and uterine wall of a pregnant female (about 14th to 15th week after conception) into the amniotic cavity.
(3) A small amount of amniotic fluid is withdrawn. It contains foetal skin cells and a number of proteins, especially enzymes. The cells can be cultured in vitro for further examination.
(1) Sex determination : The somatic cells of foetal skin drawn with the amniotic fluid are stained to determine the presence of sex chromatin (barr body). Presence of barr body indicates that the developing foetus in female as female is with 2 X-chromosomes out of which one X-chromosome is active, while other X-chromosome is heterochromatised into a darkly stained barr body.
(2) Congential disease : By Karyotypic studies of somatic cells, abnormalities due to changes in chromosome number like Down's syndrome, Turner's syndrome, Klinefelter's syndrome etc. can be determined.
(3) Metabolic disorder : By the enzyme analysis of amniotic fluid, different types of inborn metabolic disorders like phenylketonuria, alcaptonuria etc. can be detected. These inborn errors are caused by the absence or inactivity of specific enzymes due to gene mutations. So with the help of amniocentesis, if it is confirmed that the child is likely to suffer from some incurable, congenital defect, the mother can go for abortion.
(4) Drawback : However, these days, the amniocentesis is being misused also. Mothers even get their normal foetus aborted if it is a female. This is just equivalent to killing of a normal child. So Govt. of India enforced the Pre-natal Diagnostic Techniques (Regulation and Prevention of Misuse) Act, 1994, since January 1, 1994 under which all genetic counselling centres and laboratories are required to apply for registration. The violation of this Act can bring a fine of Rs. 50,000 and imprisonment for two years. The doctor's registration is also cancelled till the complaint is disposed of.
(5) Chorionic Villus Sampling (CVS) : Amniocentesis is possible without a chance of injuring the foetus with the needle only after the sixteenth week of pregnancy. At this time, abortion is not safe. A new technique, named Chorionic Villus Sampling (CVS), can be done during the eighth to tenth week of pregnancy when abortion is safe for the woman. For CVS, cells are sucked into a catheter passed through the cervix. CVS technique provides a mass of rapidly dividing foetal cells, thus facilitating the examination of chromosomal disorders.
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