Down Syndrome Testing

Down’s syndrome is a chromosomal abnormality that affects many kids. A normal human being has 46 chromosomes which are obtained equally from sperm and egg.

But in certain cases the embryo gets one extra chromosome 21 and thus the total number of chromosome becomes 47 and this abnormality in genetic makeup will be reflected in the baby’s growth and development.

Kids with Down’s syndrome may have small hands
, low set ears, eyes that slant outwards and upwards, defective heart, digestive tract defects, hearing, learning difficulties etc. As Down syndrome is very common and is leading to many family problems there are screening tests available to rule out the chances of down’s syndrome.

Screening Tests

The most common screening tests that are used for detecting Down’s syndrome are blood test and ultra sound scanning. The expected mother’s blood contains different markers which can be detected through blood test and this test is called triple screening test. The three markers are alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and unconjugated estriol (uE3).

Alpha-fetoprotein is a protein produced by fetal liver and yolk sac and a part of this gets in to the mother’s blood which can be identified through blood test. If the fetus has possibilities to develop Down’s syndrome then the level of this marker will be very less in the mother’s blood. In such cases the fetus and yolk sac are smaller than the required size and won’t be able to produce the alpha-fetoprotein.

Human Chorionic gonadotropin is a hormone produced by the placenta and a specific part of this hormone called beta subunit gets increased in case of Down’s syndrome pregnancy.

Estriol is also a hormone produced by placenta with the help of the ingredients produced by adrenal gland and fetal liver. Pregnancies which are affected by Down’s syndrome will have decreased level of this hormone in the mother’s blood.

If all these tests provides positive result for Down’s syndrome then a fourth one called Inhibin A is also conducted and the results are then compared with gestational age to determine the conclusive results.

Inhibin A being a protein is designed to inhibit the pituitary gland from producing a hormone called FSH and is produced by the ovary. Mothers having Down’s syndrome baby in their womb have a higher level of this protein in their blood

All the above mentioned test is conducted normally during 15th to 18th week of pregnancy. Sometimes another test called PAPP-A may also carried out to find Down’s syndrome possibilities.

This is the pregnancy associated plasma protein
and the protein is produced by the outer covering of the recently fertilized egg. Lower level of this protein during the first trimester of pregnancy increases the chances for having a Down’s syndrome baby.

Women above 35 years old or those having complicated pregnancies are usually recommended to under go screening tests and once the screening test provides positive results then they are subjected to diagnostic tests called amniocentesis, CVS etc. Thereafter the parents can decide whether they want to continue the pregnancy or prepare for an abnormal child.



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