According to World Health Organization, normal newborn infant' s weight is 2.5 kg. or more. There is preliminary loss of weight, during the first 10 days after the birth, due to adjustment, inadequate feeds, and digestive adaptation.
After 10 days of life, the infant gains about 30 grams per day for five to six months. The Weight gain becomes 15 gram per day during 6 to 12 months. After the age of one year, weight gain may be 2 to 3 kg. per year.
At the age of six months, the weight is 5 to 6 kg. (doubles the birth weight). At the age of one year, the weight is 7.5 to 9 kg. (trebles the birth weight. and the birth height approximately trebles, at the age of 13 years Birth height doubles, at the age of 4 years and becomes 100 and the birth height approximately trebles at the age of 13 years.
B. Head Circumferences:
Head circumference is related to the rate of the growth of the brain. In the newborn, it is 2 cm. Smaller than the chest circumference. At birth, it is 33 to 35 cm., at 3 months, about 40 cm., and at 12 months, 45 cm. It is abnormally large in hydrocephalus, and abnormally small in macrocephalus.
C. Chest Circumference:
The chest is barrel shaped at birth, and anteroposterior and transverse diameters are equal. Gradually, the transverse diameter increases. At the end of the one year of the age, head circumferences and chest circumference are equal. Then, the chest circumference increases.
D. Body Proportions:
At the birth, the midpoint of the body is 1.8 cm. above the umbilicus, at two years, it is just below the umbilicus, and at the age of 16 years, the midpoint is near the symphysis pubis. The relation of head and trunk to the lower extremities is 1.7: 1 at birth, which becomes 1:1 at the puberty.