What is the cause for down syndrome?

I didn't find a forum about this subject and wanted to ask a question. I've heard so much about down syndrome, like young people could have a kid wit DS, or a much older woman, etc etc. But of course science says there's no way to know how it happens or if it can be prevented. Although I believe that God has a lot to say in these things, I also believe that we need to be wise as to what we eat and how to take care of our bodies.

What worries me is that my mom had a brother who had DS, very mild, but my grandma didn't have him maybe until the late 30's (age wise I mean). So if it runs in the family, then it's in my genes. I'm 34 and my husband and I are planning to get pregnant by next year and I don't know if I'm at risk, if it's something to do with my lifestyle that causes it and if I could prevent it. Is there anything I can do? Please help!! Thanks. Tweet