Section 1, Article 1 - Infants may grow and develop at their own individual rate, but growth in the life of a human typically follows two lines of development. Cephalocaudal development is the tendency for growth to follow a sequence in which development moves from top to bottom. For example, a child’s head develops much sooner than his or her legs. This is true both in terms of physical growth and motor development. Proximodistal growth is the body’s tendency to grow from the center of the body outward to the extremities.
In the United States, 96% of children born in 2010 weighed between 4.4 pounds and 9 pounds. The average length of a newborn is 20 inches (). Interestingly, infants typically lose 5-7% of their birth weight within the first day or two after birth. Following this initial loss, healthy children regain this lost weight in the first week, then begin steady weight gain. By a child’s fourth month their weight will typically double. By the time they celebrate their first birthday their weight will have tripled. Height progresses at an equally dramatic pace. Most children grow at a rate of about ¾ of an inch each month during the first year, increasing their birth length by about 40%. The rate of growth slows considerably in the second year, but by age two, a child will have achieved approximately half their adult height, and 1/5 of their adult weight.
Growth in infancy is closely monitored. Regular well-child visits typically consist of measuring the child’s height, weight, and head circumference. This information is then compared to measurements from previous visits, and to standardized charts that show typical growth rates. The comparison to previous visits will tell if the child is progressing; the growth charts will tell how the child compares to his or her peers. This comparison is often expressed in a percentile ranking from 0 to 100. For example, if a child is in the 25th percentile for weight it means that 25% of all babies weigh less and 75% weigh more. A consistently accelerated growth pattern may indicate a risk for developing obesity later in life (). On the other hand, a child that is not gaining weight and/or growing at the expected rate may indicate failure to thrive.