What is Down’s syndrome?
Down’s syndrome is a type of chromosomal abnormality which is characterised by an extra copy of chromosome 21. This results in a total of 47 chromosomes in each human cell rather than 46 chromosomes, as is seen in normal individuals. The extra chromosome can either be a complete chromosome or a partial chromosome and the extra genetic material present is cause of the many characteristics seen in children with Down’s syndrome, including congenital heart defects and a number of possible medical conditions.
How does the test work?
This screening test only requires a medical blood draw from the expectant mother. Once your sample is received, the cell free fetal DNA in the same will be analysed to confirm or exclude Down’s. Scientists analyse the foetal DNA in the maternal blood sample to establish the ratio of foetal chromosomes. We know that if the expectant mother is carrying a child with Down’s syndrome, the ratio of genetic material associated with chromosome 21 will be higher due to the extra, 3rd copy of that chromosome.
It is important to note that the NIPT is a screening test and not a diagnostic test. This test cannot replace diagnostic tests such as amniocentesis or chorionic villus sampling although it can help pregnant women avoid the need to undergo these tests.
What are my chances of having a child with Down syndrome?
Down syndrome manifests itself in all cultures and ethnic groups. Age is however an important factor.
- 35 year old woman has about a one in 350 chance of conceiving a child with Down syndrome
- From the age of 40, the chances of having a Down syndrome child are around 1 in 100.
Down’s syndrome is not hereditary and only around 1% of all Down syndrome cases have a hereditary component.
Will I still need a diagnostic test?
Down’s syndrome can be diagnosed with invasive tests like amniocentesis and chorionic villus sampling. These tests however, carry certain risks. If the non invasive blood screening test gives a positive result, your health care specialist might still suggest prenatal diagnostic testing via amniocentesis or CVS. Because the (NIPT) test is so accurate and sensitive, if the result proves an extremely low probability for Down’s syndrome then you will not need to undergo any diagnostic tests.
All expecting mother’s can carry out the non invasive prenatal test for Down syndrome without exception.