Check with you doctor or a nurse and see if they know of any petite prenatal pills. There were some in my pack of samples, but I don't remember what they were called.
The best way to get vitamins is through foods. Pills only a very small %age of them is actually accepted into your system (hence the amount of vitamins in them being huge). If you find you're lacking something find a food that contains it.
Can you cut them in half? My prenatal vitamins are pretty large but not sure if they make a smaller size. Do they have chewable/gummy ones out yet?