Baby fontanel is small, as long as the head circumference is normal, then it is usually normal, in addition, microcephaly, narrow skull syndrome can also lead to the baby to appear pathological fontanel small performance. 1. Physiological factors: the baby fontanel small may be a normal phenomenon, the baby’s posterior fontanel is relatively small, usually 6 to 8 weeks after birth can be closed, the baby’s anterior fontanel will be closed at the age of one year to one and a half years old or so, so if the baby is already 8 to 9 months old, fontanel is small but the head circumference is normal, this is completely normal, do not need to worry too much. 2. Microcephaly: Microcephaly can lead to the symptom of small fontanel, and this baby will also be accompanied by a head circumference smaller than that of children of the same age. The baby’s head circumference should be about 34cm at birth, 43cm when the baby is 6 months old, 46cm when the baby is one year old, and 48cm when the baby is two years old, and if it is less than 5% of the average, then we need to be vigilant. 3. Craniosynostosis: Craniosynostosis is also known as premature closure of the cranial sutures. Children with this disease may have the symptom of a small fontanel, and may also have a small head circumference, head deformity, mental retardation and other manifestations. After eliminating physiological factors, if you find that your baby has a small fontanel, you have to consult a doctor in time to find out the cause and ask the doctor to deal with it.