![]() A screening test can tell a woman and her healthcare provider whether her pregnancy has a lower or higher chance of having Down syndrome. There are two basic types of tests available to detect Down syndrome during pregnancy: screening tests and diagnostic tests. 3-5However, the majority of babies with Down syndrome are born to mothers less than 35 years old, because there are many more births among younger women. Women who are 35 years or older when they become pregnant are more likely to have a pregnancy affected by Down syndrome than women who become pregnant at a younger age. One factor that increases the risk for having a baby with Down syndrome is the mother’s age.Researchers know that Down syndrome is caused by an extra chromosome, but no one knows for sure why Down syndrome occurs or how many different factors play a role. The extra chromosome 21 leads to the physical features and developmental challenges that can occur among people with Down syndrome.However, they may have fewer features of the condition due to the presence of some (or many) cells with a typical number of chromosomes. Children with mosaic Down syndrome may have the same features as other children with Down syndrome. For children with mosaic Down syndrome, some of their cells have 3 copies of chromosome 21, but other cells have the typical two copies of chromosome 21. Mosaic Down syndrome: This type affects about 2% of the people with Down syndrome.2 This occurs when an extra part or a whole extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome rather than being a separate chromosome 21. ![]()
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