The main indicators to evaluate the size of the fetal head are the biparietal meridian and fetal head circumference. A large fetal head is defined as the biparietal diameter or head circumference of the baby’s head that is found to exceed the upper limit of the normal reference range of fetal biparietal diameter and head circumference at the same gestational week during fetal ultrasound measurements. The cause of a large fetal skull may be genetic. If one of the parents has a large skull, the baby may have a large head. It can also be caused by congenital abnormalities in the baby’s skull, which are commonly seen in babies with hydrocephalus, where enlarged ventricles can be found during ultrasound examinations. It can also be seen in babies with intracranial occupying lesions, which can be found during 4D ultrasound screening to reveal an enlarged skull with intracranial cysts or substantial tumors.