Abnormal head shape can result from pressure on the head during a head-first delivery.

Compared to an adult, a newborn's head is large in proportion to the rest of the body, usually about 1/4 of the body surface area. The bones of the skull are soft and pliable with gaps between the plates of bone. These gaps close as the bones grow and the brain reaches its full size. The spaces between the bony plates of the skull are called cranial sutures. There are two gaps that are particularly large, the anterior and posterior fontanelles. These are the soft spots you can feel when feeling the top of your baby's head.

During a head-first delivery, pressure on the head caused by the tight birth canal may "mold" the head into an oblong shape. Depending on the amount and duration of pressure, the skull bones may even overlap. In addition, during this most common (and overall safest) type of delivery, fluid may collect in the scalp (caput succedaneum) or even blood beneath the scalp (cephalohematoma) of the baby. This may further distort the shape and appearance of the head. Although typically a source of much concern for new parents, fluid and blood collection in and around the scalp is a common occurrence during delivery and usually disappears after a few days.

If your baby is born breech or with delivery by cesarean section, the head is usually round and otherwise well shaped.

Extreme abnormalities in head size are NOT related to molding. See microcephaly (abnormally small head size) and macrocephaly (abnormally large head size).