1 and a half year old baby head circumference if physiological factors, do not need special treatment, if it is a pathological factors, such as vitamin D deficiency, hydrocephalus, etc. to actively cooperate with the doctor, to take general, drug and surgical treatment and so on. 1. Physiological factors: under normal circumstances, the proportion of the baby’s head circumference is different from that of adults, and the head circumference will be relatively large, especially affected by genetic factors, some babies because their parents’ head circumference is large, and they may also inherit this situation, which does not require special treatment. 2. Vitamin D deficiency: when the body of vitamin D deficiency, the baby is prone to calcium deficiency, thus causing rickets, which affects the baby’s head development, resulting in head circumference, need to follow the doctor’s advice to supplement vitamin D in a timely manner, and pay attention to more sunshine, promote vitamin D absorption. 3. Hydrocephalus: hydrocephalus can also lead to an abnormal increase in the baby’s head circumference, if not taken in time to treat, will lead to the baby’s intellectual decline, limb movement disorders, etc., generally need timely surgical treatment. 1.5 year old baby head circumference, if accompanied by other uncomfortable symptoms, should be timely to the hospital, to identify the causes of targeted treatment.