Conversation so far:
how does the placenta detaches from the uterus after birth
Placental expulsion begins as a physiological separation from the wall of the uterus.
which stage of labor is the expulsion of the placenta
The period from just after the baby is expelled until just after the placenta is expelled is called the third stage of labor.
what happens to the placenta after expulsion
In some cultures the placenta is kept and consumed by the mother over the weeks following the birth. This practice is termed placentophagy.

Question: what happens if the expulsion does not occur
Self-contained rewrite: what happens if the placenta expulsion does not occur