I have had a couple of miscarriages and i know how you feel! I was SO paranoid when i got pregnant with Ella! I now have a perfectly healthy happy 16 month old, and planning on the second baby at the moment!
think positively! I started 'talking' to Ella very early on, and that helped me deal with my fear, and bond with her, and i did everything i could to make myself as healthy as possible.
I was taking the best pre-natal vitamins i could find (Elevit by Roche) eating right, sleeping right etc etc etc.
I was also in a lot better place emotionally and physically when i fell pregnant with Ella and i think that made a big difference.
just try to relax and stay on top of your fear.
Its perfectly natural to worry.
how far along are you?