What if?

I am sitting here in my "Alternate Behaviors in Young Children" class (where I should be paying attention to the presentation, but they have free Wi-Fi and I have a laptop). Which is basically a class for Special needs children. All I can think about is, What if I do get pregnant? What if my child has ton's of problems? What if we can't afford the care to handle it? What will I do to take care of them?
Oh my goodness so many "what if" questions! I don't even know if I'm pregnant and these questions flood my mind with worries. Mike and I had talked about life with a Down's child, we know that's a possibility because of our ages, and we think we can handle that. But what about CP or some other awful medical malady that we have no control over.
I guess we just have to take a chance and jump in. Is that what every parent does? Do young parents just assume their child will be fine and have no troubles? I guess it's all up to fate.
Sometimes I take my worries to the worst case scenario so I can work out a plan in my head. 99% of the time those worst case scenarios never happen (except for being able to get pregnant - and we're dealing with that), but just in case it does I like to have at least pondered the idea.
EGADS the responsibility of even just getting pregnant - sheez!