One problematic position is when the placenta drops too low and gets in the way of childbirth. This low-lying placenta is common during the second trimester, but will typically move before actual childbirth. The placenta does not move so much as repositions depending on the growth of the womb and the placenta itself.
If the placenta does not reposition, then there is a higher possibility for early labour and bleeding. Sometimes the bleed could be severe. The blood comes from the mother, not the baby, so your infant would not do any harm. Your doctor will do an ultrasound at about 32 weeks to ensure the placenta is no longer in the way. Only a very small percentage, less than one percent, will remain low-lying towards the end of pregnancy.
If there is continued concern over the placenta or bleeding, and it does not appear it will move out of the way for the birth, your baby will have to be delivered via c-section.