Obstetrical Hemorrhage 4. The other major cause of third trimester bleeding is placental abruption.
Placental abruption is separation of the placenta from the implantation site.
This may be partial, or it may be complete. Initially partial abruption may progress to complete abruption at any time. Click here for a larger view. Ultrasound of placental abruption. The fetal body and bladder are labeled FB, and BL, respectively.