Babies have big heads to hold rapidly growing brains. A 2-year-old's brain is 80% of adult size.
Babies' brains grow by 1 percent each day beginning right after infants are born, according to a new study that aimed to map newborns' brains during their first three months of life.
Researchers scanned the brains of 87 healthy newborns 211 times, starting when the babies were only 2 days old. They found that the newborn brain grows extraordinarily fast right after birth, but slows down to a growth rate of 0.4 percent per day by the end of three months.
Overall, infants' brains grew by 64 percent in the first 90 days, according to the study. The average brain size was 20 cubic inches (341 cubic centimeters) at birth, and 34 cubic inches (558 cubic cm) at 90 days. In other words, the brains of newborns grew from about 33 percent of the average adult brain size to 55 percent of it in three months.
The researchers noted that the brains of the infants who were born one week earlier than the average in the study (about 38 weeks), were 5 percent smaller than the average.