What are the recommended genetic tests for Down Syndrome diagnosis?

Universal screening for Down syndrome should be done for every pregnancy, irrespective of family history or maternal age. It is untrue that only women above 35 years of age can have a child with Down Syndrome. It can happen to women of all ages. The main genetic cause of Down Syndrome is due to an extra copy of Chromosome 21, called as Free Trisomy 21. Another cause could be movement of part of chromosome 21 to a different chromosome number, called as Translocation Down syndrome. Most of the Free Trisomy 21 cases happen without a family history, and happen by a chance event. Recurrence risk for Down syndrome, due to Chromosome 21 translocation, in the second child is high if parents are carriers of the translocation. First child with Down Syndrome must undergo genetic testing to know the kind of Chromosome 21 abnormality. Recurrence risk for Down syndrome, due to extra copy of Chromosome 21, in the second child is very low (less than 1%). If the first child has Down Syndrome, the mother is tested during 16weeks of pregnancy for Chromosome 21 abnormalities in the second pregnancy. If the first child has translocation Down syndrome, both the pregnant mother and father are genetically tested for Chromosome 21 translocation, by Amniocentisis of fetus and Karyotyping of foetus and parents. For the first pregnancy without any family history of Down syndrome, the woman must undergo a battery of tests as part of her first trimester screening and is given a report that either indicates low or high risk for Down syndrome. If the risk for Down syndrome is high in the first trimester screen, invasive tests such as Aminocentisis or Chorionic Villus sampling is done to see specific defects for the condition. Second trimester screening is also done in some cases through quadruple marker testing. Non-invasive prenatal tests are also being used as a screening test with a high detection rate for Down syndrome genetic defects.

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