Newborns concave in the back of the head is considered to be the posterior fontanel, but also may be caused by brain dysplasia, trauma and so on. 1. Posterior fontanel: The depression at the back of the head of a newborn is usually a posterior fontanel structure, a part of the skull that is not completely closed. 2. Brain dysplasia: A small number of newborns have a concave back of the head, which may be due to brain dysplasia caused by maternal infections or other illnesses during the embryonic period, and the skull is relatively small, and the back of the head will have a slight concave phenomenon. 3. Trauma: It is possible that a newborn baby suffers from trauma, such as a fall that injures the occipital region, which may lead to a concave back of the head. Newborns with concave back of the head, there may also be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.