At the 28week scan make sure you ask for a colour doppler and they check for vasa previa.
I just had a baby 2 weeks ago and spent from just before 30 weeks until delivery at 35 weeks in hospital due to vasa previa. It is a very serious condition.
Prior to 30 weeks I was told I had placenta previa only.
If it is only placenta previa then you have loads of time for the placenta to move out of the way.