Final answer:
Changes in the shape of the uterus, such as becoming more globular and rising in the abdomen, indicate that the placenta has separated and is ready for delivery, marking the end of the final stage of labor and the beginning of the postpartum period.
Step-by-step explanation:
The observation that would indicate the placenta has separated from the uterine wall and is ready for delivery is changes in the shape of the uterus. An essential sign is when the uterus becomes globular and rises in the abdomen as the placenta moves into the vagina. Also, a sudden gush of blood and lengthening of the umbilical cord can signal placental separation. These events prompt the final stage of labor, where the placenta and associated membranes are delivered. This process marks the transition to the postpartum period, during which the mother's body returns to a non-pregnant state.
After the delivery of the newborn, the placenta's detachment via continued myometrial contractions is crucial in preventing postpartum hemorrhage. The obstetrician must examine the expelled placenta to ensure no fragments remain, as they might cause hemorrhage if not properly managed. The uterine contractions also contribute to the involution process, helping the uterus to return to its pre-pregnancy size.