Final answer:
The primary nursing action in the third stage of labor is assisting with the delivery of the placenta. Monitoring vital signs, providing emotional support, and administering oxytocin if necessary are also important but secondary to assisting with placental delivery. Hence, option (3) is correct.
Step-by-step explanation:
The major nursing action for the third stage of labor, which is the delivery of the placenta after the baby has been born, is assisting with the delivery of the placenta. This stage can last from a few minutes to a half hour, during which the placenta and associated fetal membranes are expelled.
Nurses may also monitor vital signs, provide emotional support, and in some cases, administer oxytocin if needed to facilitate the passage of the placenta. However, assisting with the delivery of the placenta is the primary focus to ensure that it has been completely disengaged from the uterine wall and is delivered safely.
Notably, administering oxytocin can be part of the protocol in this stage to prevent hemorrhage, but the administration occurs after the placenta is delivered or if there is a need to facilitate its delivery.