Abruptio placentae usually occurs during pregnancy. The uterus is enlarged, tense, symmetric, contains the fetus, and usually contracts. The fetus is felt vaginally through the cervix, and no tear is palpable.
On the other hand, rupture of the uterus usually occurs during labor, unless after a cesarean section. The uterus is small, at one side, with an adjacent symmetric mass, and the fetus is easily outlined. There are no uterine contractions and a tear may be felt vaginally.