M.F.
Yes it's safe to have your filling replaced. It's my understanding as a nurse and mom who breastfed my two girls that the mercury is chemically bound and thus unable to be absorbed into your system (and your babies) in any appreciable amounts. You are probably at a greater health risk not fixing your teeth. Cracked fillings are the perfect breeding grounds for all kinds of bacteria that can cause both of you a lot more harm. Call your dentist!