The
severity or grade of placenta previa will usually determine how serious the condition is, how much bleeding is expected and if a vaginal birth is possible. The main health concerns include:
The heaviness of the bleeding. It can be difficult for caregivers to tell where the vaginal bleeding is actually coming from. Sometimes it is from the woman's uterus or it could be from the placenta (affecting the baby). With placenta previa it is also possible for bleeding to come from both the woman (where the placenta is attached) and the placenta. Occasionally, the caregiver performs a test on the vaginal blood coming away, to try and tell if it is coming from the woman or the placenta.
Blood loss from the woman can contribute to her being anaemic and having a low blood pressure. If very severe, it can be life-threatening for her (although this is rare with placenta previa). Blood loss from the placenta can affect blood flow to the baby and the transport of oxygen and nutrients to the baby. If bleeding is severe, it can cause the baby distress or in some cases be life-threatening for the baby.
Reduced growth for the baby. A low-lying placenta may affect the level of oxygen and nutrients the baby receives. This is because the lower segment of the uterus (where the placenta is implanted) is thinner muscle, usually only designed to absorb the cervix during labour. The lower segment has less blood supply than the upper segment, and therefore may not nourish the baby as efficiently. It is more difficult for the placenta to implant properly into the lower segment, and also more likely parts of the placenta will separate from the wall of the uterus during bleeding (meaning less placental tissue being able to function efficiently). You can read more in
small for gestational age babies.
A premature baby. Bleeding from placenta previa can stimulate premature labour, and contractions from premature labour can in turn stimulate heavier bleeding.