Question

explain, in your own words, the difference between the following types of analysis: karyotype, amniocentesis, Chorionic villus sampling and non-invasive prenatal diagnosis. Give advantages and disadvantages to each testing type. Why are these tests used and under which circumstances might one test be used over another?

Answer 1

Step 1

Every organism has definite set of chromosomes in each cell. Humans have 46 (23 pair ) of chromosomes in each cell. Sometimes, this number may be increased or decreased or some part of chromosome is missing or new one is inserted due to mutation or other factors, by which there is abnormalities in the chromosomes and therefore, in the whole human body. So, to check these abnormalities in the developing foetus doctors prescribe some prenatal laboratory tests or screenings to detect these chromosomal abnormalities. It includes various kinds of tests such as:-

Step 2

Karyotype :- Karyotype is the complete set of chromosomes in an individual. Analysis of karyotype to detect or identify any kind of abnormalities in the chromosomes is called karyotype analysis. In this, it is checked that whether the growing foetus have complete set of chromosomes, is there any extra chromosome or is there any deleted chromosome. Karyotype analysis helps in detection of genetic disorders like Down syndrome, Edward syndrome, Turner syndrome etc . Karyotyping can be done by :-

Step 3

Chorionic villus sampling is also a prenatal laboratory Karyotyping screening or test in which a sample of chorionic villi is removed from the placenta for Karyotyping i.e chromosome analysis. The sample can be taken through the cervix or the abdominal wall. It helps in detection of genetic disorders like down syndrome, Edward syndrome etc.

Step 4

Amniocentesis is a prenatal screening test in which a small amount of amniotic fluid is removed from the sac surrounding the fetus for testing. The sample of amniotic fluid is ducked through a fine needle inserted into the uterus through the abdomen. The fluid is then analysed in the laboratory. Amniocentesis is performed to look for certain types of birth defects or disorders such as Down syndrome, a chromosomal abnormality or sex of the growing foetus. Sometimes, there is chance of miscarriage, or preterm labor during this test which is disadvantage.

Non-Invasive Prenatal Testing popularly known as NIPT is a DNA screening test to check the chance that the developing foetus has Down syndrome or another chromosomal abnormality like trisomy of chromosome 18, trisomy of chromosome 13 or an extra or missing sex chromosome. NIPT diagnose particularly the down syndrome, which is a genetic disorder caused due to the trisomy of chromosome 21 means there is extra copy of chromosome number 21.