Plagiocephaly can develop while the baby is in the womb (intrauterine) or after delivery. One intrauterine cause is the lack of space during late stages of pregnancy. The baby’s head may be compressed at one side as a result of limited space, causing a relatively flatter skull on the pressured side. Thus, plagiocephaly is more common during the first pregnancy and multiple pregnancy.
Most plagiocephaly happens after delivery. In 1992, prone lying was identified as a factor that may cause Sudden Infant Death Syndrome (SIDS). As a result of SIDS prevention, parents position their baby on their back for play and sleep. This has successfully reduce SIDS incidence worldwide. However, this also caused many babies to developed pressured spot on their skull while lying on their back, resulting in development of plagiocephaly.
Plagiocephaly is also related to torticollis. Torticollis is a condition where certain neck muscle is shortened, causing the head to rotate and/or side tilt. This preferential head rotation results in flattening of the skull on the pressured side. Infants with macrocephaly and/or low muscle tone (hypotonia) tend to develop plagiocephaly due to the lack muscle strength to rotate or control head movement. The flattened skull also encourage the child to lie on it even more as it is a position of comfort. As a result, the deformity is maintained.