Final answer:
The nurse should reassure the new mother that the cone-shaped head of her newborn is due to the flexibility of the skull during birth and will round out in a few days, as this is a normal occurrence caused by fontanels.
Step-by-step explanation:
The appropriate response from the nurse to the new mother's observation about her baby looking like a "conehead" is number 4: "This often happens as the baby's head moves down the birth canal; the bones move for easier passage." This phenomenon is due to the presence of fontanels, which are soft spots in the neonate's skull that allow the head to be flexible during birth for easier passage through the birth canal. After birth, the head shape begins to normalize as these fontanels eventually ossify and the skull bones settle into a more rounded shape.
Within the first few days to weeks after birth, you can expect the newborn's head shape to become rounder. It is important to provide reassurance to new parents that this temporary conical head shape is normal and will resolve on its own.