Which action is essential when caring for a mother during delivery when the head is visible?

Applying pressure to the perineum is essential when caring for a mother during delivery when the head is visible because it helps to support the perineum and reduce the risk of tearing. This technique, known as perineal support, can provide stability and prevent excessive stretching of the tissues as the baby's head crowns. By providing gentle pressure, the caregiver can help guide the baby's head out more gradually, which can increase the likelihood of a controlled delivery and minimize trauma to the perineum.

In this situation, other actions such as encouraging the mother to push forcefully can lead to a rapid delivery, which might increase the risk of tearing and complications. Checking for signs of fetal distress is important throughout labor but may not be the immediate priority once the head is visible. Preparing for an episiotomy, while sometimes indicated, is not always necessary and should not be a standard action at this stage without clear indications for such a procedure.