Hi, I had gone through your question and understand your concerns Average head circumference of a 9.5 month baby is 44-45 cm. If everything is normal , means physical examination and development normal ,it does not seem to be reason of big concern . Ultrasonography of brain ( if anterior fontanelle is open) , can be done to rule out hydrocephalus , chances of which are minimal in a normal child . Most common cause of large head in a normal child is familial , ( feature present in other family members) or Idiopathic and also in big baby . You can discuss doing a ultrasonography of brain with your doctor , if he/she considers it to be done , it can be done to be sure that we are not missing anything. Keep a watch on development of your child. Hope this answers your question. If you have additional questions then please do not hesitate in writing to us. Wishing your baby good health.