Читать книгу Lifespan Development - Tara L. Kuther - Страница 200

It is easy to observe that infants grow substantially larger and heavier over tim—but there are many individual differences in growth. How can parents and caregivers tell if a child’s growth is normal? By compiling information about the height and weight of large samples of children from diverse populations, researchers have determined growth norms. Growth norms are expectations for typical gains and variations in height and weight for children based on their chronological age and ethnic background.

In the first few days after birth, newborns shed excess fluid and typically lose 5% to 10% of their body weight. After this initial loss, however, infants gain weight quickly. Infants typically double their birth weight at about 4 months of age, triple it by 12 months, and quadruple it by 2.5 years (Kliegman et al., 2016). The average 3-year-old weighs about 31 pounds. Gains in height of 10 to 12 inches can be expected over the first year of life, making the average 1-year-old child about 30 inches tall. Most children grow about 5 inches during their second year of life and 3 to 4 inches during their third. To parents, growth may appear slow and steady, but research has shown that it often occurs in spurts in which an infant or toddler can grow up to one quarter of an inch overnight (Lampl, Johnson, & Frongillo, 2001). Infant growth appears to be tied to sleep as increased bouts of sleep predict small bursts of growth (Lampl & Johnson, 2011). At about 2 years of age, both girls and boys have reached one half of their adult height (Kliegman et al., 2016).

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Figure 4.1 Body Proportions Throughout Life

Source: Huelke (1998).

Growth is largely maturational, but it can be influenced by health and environmental factors. Today’s children grow taller and faster than ever before, and the average adult is taller today than a century ago. Increases in children’s growth over the past century are influenced by contextual changes such as improved sanitation, nutrition, and access to medical care (Mummert, Schoen, & Lampl, 2018). Large gains have occurred in North America and Europe, followed by South Asia (NCD Risk Factor Collaboration, 2016). Although children of sub-Saharan Africa showed growth gains into the mid-1990s, mass poverty and starvation, poor infrastructure to provide clean water and sanitation, and exposure to the emotional and physical stresses of war and terror have affected growth (Simmons, 2015). Good nutrition is critical to healthy growth during infancy and toddlerhood. Many infants’ first nutritional experiences are through breastmilk or formula.