Growth is very rapid, especially during the initial 6months. Infants gain 150 – 210g (5 – 7 ounces) weekly until approximately age 5 to 6 months, when the birth weight has at least doubled. An average weight for a 6-month-old child is 7.26Kg(16lbs). Weight gain slows during the second 6 months. By 1 year of age, the infant’s birth weight has tripled. Infants who are breast-fed beyond 4 – 6 months of age typically gain less weight than those who are bottle-fed, yet head circumference is more than adequate.
Height increases by 2.5cm (1inch) a month during the first 6 months and also slows during the second 6 months. Average height is 65cm(25.5inches) at 6months and 74cm(29inches) at 12months. By 1 year, the birth length has increased by almost 50%. This increase occurs mainly in the trunk, rather than in the legs, and contributes to the characteristic physique of the infant.
Head growth is also rapid. During the first 6 months, head circumference increases approximately 1.5cm(0.6in) per month but decreases to only 0.5cm(0.2in) monthly during the second 6 months. The average size is 43cm (17in) at 6 months and 46cm(18in) at 12 months. By 1 year, head size has increased by almost 33%. Closure of the cranial sutures occurs, with the posterior fontanel fusing by 6 to 8 weeks of age and the anterior fontanel closing by 12 – 18months of age ( the average age being 14 months).
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