A classic difference between abruptio placentae and placenta previa - major role of the placenta is to function as a fetal lung

- A classic difference between abruptio placentae and placenta previa is the degree of pain. Abruptio placentae causes pain, whereas placenta previa causes painless bleeding.

- Because a major role of the placenta is to function as a fetal lung, any condition that interrupts normal blood flow to or from the placenta increases fetal partial pressure of arterial carbon dioxide and decreases fetal pH.