No - once the placenta is attached, its attached. It may shift as your uterus grows, but it is more or less stable. I don't know for sure if there is any danger associated w/ it being in the front - I think it is usually near the top at the back wall. The only dangerous positions I'm aware of are at the very top (it heightens the risk of a very, very sickening complication that, without going into much detail, threatens the uterus at the time of birth), and at the bottom, covering the cervix. But like I said, those are the only ones I'm aware of - there may be more.
at 2:00 AM on Dec. 5, 2009