What is the range of normal child’s head circumference: brain growth during the fetal period is in the lead of all systems, so the head circumference at birth is relatively large, averaging 32-34cm; similar to weight and length growth, the growth of head circumference in the first 3 months of the first year (6cm) is approximately equal to the growth value of head circumference in the second 9 months (6cm), i.e., the head circumference at the age of 1 year is about 46cm; the growth of head circumference in the second year after birth slows down to about 2cm; the head circumference at the age of 2 is about 48cm. The measurement of head circumference is most valuable within 2 years of age. Head circumference reflects brain volume: head circumference is closely related to brain development, and some people compare the human brain to a “walnut”, which seems appropriate. People can not accurately measure the weight of the brain, the size of the head circumference, can reflect the volume of the brain of the child. Therefore, by measuring the baby’s head circumference, you can indirectly understand the status of the baby’s brain development. A small head circumference suggests that the baby’s brain is limited or stunted by a too small skull; a large head circumference suggests fluid retention in the brain or other factors that can cause brain cell enlargement, so measuring the head circumference, although an easy and simple method, has considerable significance. Head circumference is too large to be alert: normal baby cranial cavity mainly has brain tissue, cerebrospinal fluid, cerebral vessels and blood flowing in its lumen, the volume of the cranial cavity and the volume of its contents is constant, and the pressure inside the cranium is maintained at a certain level. If the baby’s head circumference is too large, the possibility of hydrocephalus, brain tumor, encephalitis and other disease lesions will increase. Therefore, parents should be alert if the baby’s head circumference is too large or increases abnormally fast. Since the skull sutures of children are not yet closed, they can open up when the pressure inside the skull increases and the head circumference increases. Therefore, parents should pay attention when they find that the child’s head circumference is significantly larger than the surrounding children of the same age. Pay attention to whether the child has congenital hydrocephalus, because children with hydrocephalus have a rapidly enlarging head within a few weeks or months of birth, with head circumference far exceeding the normal range. There are also problems with a small head circumference: for example, the influence of harmful factors such as infection, malnutrition, poisoning and radiation in the mother’s early pregnancy can affect the cranial development of the fetus. If the child itself suffers from metabolic diseases, chromosomal aberrations, etc. can also cause microcephaly in the child. If the child suffers from trauma or infection during or after birth, it can cause brain atrophy, which can also make the head circumference smaller. In some cases, microcephaly is familial and is called familial microcephaly. A small head circumference inevitably limits the development of the child’s brain. Usually, children with microcephaly have small, pointed heads and narrow foreheads, and may be physically and mentally retarded. However, not all children with microcephaly are mentally retarded, and about 7.5% of children with head circumference 2-3 standard deviations below normal have normal intelligence. Head circumference measurement method: Use a soft measuring tape to measure the circumference of the baby’s head, starting from the arch of the eyebrow, going around the upper edge of the ears and behind the occiput, and returning to the starting point.