No. Prenatal vitamins contain the exact amount of daily vitamins that are essential for you and the baby, to the contrary, multivitamins may contain more of some certain vitamins that may not be safe.
Typically not. As long as the purity of the ingredients are verified and you don't exceed the recommended daily allowances you should have no problem. However, it is recommended that you take extra folate (folic acid) to prevent neural tube defects.
No. None that I've ever heard of.