Down syndrome are very common. Most of us have 23 pairs of chromosomes in each cell. Individuals with Down syndrome have one extra chromosome 21 in their cells. Down syndrome occurs most often by chance and is seldom inherited from parents. Down syndrome is a condition with mental handicap and certain physical features different from other people. Some children with Down syndrome have abnormality such as heart defects. With special care and education, some of them can integrate into normal schools and lead semi-independent lives. if you know the condition before birth, this would allow parents and doctors to discuss options to the best interest of the family.

A more accurate screening test called NIPT (non-invasive prenatal test) is now available.

People normally have 23 pairs of chromosomes in each cell. Each chromosome is made up of a coil of DNA. Besides her own DNA, mother’s blood also contain small amount of fetal DNA. Therefore, it allows accurate screening for fetal Down syndrome using mother’s blood. If the baby has Down syndrome, the test will show increased amount of DNA from chromosome 21. It also detects Edward syndrome (an extra copy of chromosome 18), Patau syndrome (an extra copy of chromosome 13), Turner syndrome (only 1 copy of chromosome X) and some common microdeletion problems (eg. 1p36 deletion syndrome, 2q33.1 deletion syndrome, 22q11 deletion syndrome (include DiGeorge syndrome), Angelman syndrome, Cri-Du-Chat syndrome, Langer-Giedion syndrome and Prader–Willi syndrome.

NIPT detects around 99 out of 100 Down syndrome, the accuracy of the test as described above is based on the requirement of the tested baby contributing adequate amounts of DNA into the maternal plasma sample. Therefore, it can only carried out if fetus is more than 10 weeks of gestation.