You are correct that the screenings are not always accurate. I know people who had positive results and the baby did not have Down syndrome. I, myself had a triple screen and ultrasound which was completely normal and our little boy was born with Down syndrome. The only way to know absolutely is an amniocetisis.
So, I can only tell you that having a child with Down syndrome is not the life that you envision before you have a child with a disability. These kids teach you things you never knew you needed to know. You will love your child just like any other child.
I'm so happy to hear that you do not believe in abortion. Living with an unknown is very stressful, but if you find out that your baby does or has a high liklihood of having Down syndrome, I would encourage you to contact the Down syndrome Association of Minnesota at www.dsamn.org. They are incredible people and you will be so surprised at how much support and information is out there.
I've talked with several parents just after they got a diagnosis and were in a "grieving" period. I always tell them "I'm going to talk to you a year from now and I gaurantee that your outlook on this will be completely different and you'll wonder how you ever felt this way about the incredible kid you have."
Please feel free to keep in contact with me if you want someone to talk with or to find out more about Down syndrome or special needs. Don't feel you need to handle this yourself. There is lots of support out there: people to talk with, other moms, etc. The special needs community is a very close-knit, loving community that is always willing to help someone out.
You can email me at ____@____.com.