This video talks about screening for it.

Honestly you should think twice about wanting a baby at 20.  I mean no disrepeck but I'm just sayin.  But definitely get screened...I did and thankfully things are looking good.

I don't know if you are married or in a relationship but the first thing you should do is talk to a genetic counselor about this. There are many factors that come into play involving your health, your genetics and the genetics of the father. You also need to talk to your doctor about your health and the effects that a pregnancy could have on it. Good luck and time to consult the medical experts.