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(See also Miscellaneous Disorders in Infants and Children: Failure to Thrive.)

Physical growth includes attainment of full height and appropriate weight and an increase in size of all organs (except lymphatic tissue, which decreases in size). Growth from birth to adolescence occurs in 2 distinct phases. The 1st phase (from birth to about age 1 to 2 yr) is one of rapid growth, although the rate of growth decreases over that period. In the 2nd stage (from about 2 yr to the onset of puberty), growth occurs in relatively constant annual increments. Puberty is the process of physical maturation from child to adult. Adolescence defines an age group; puberty occurs during adolescence. At puberty, a 2nd growth spurt occurs, affecting boys and girls slightly differently. All growth parameters can be charted on standard growth curves available from the Centers for Disease Control and Prevention at www.cdc.gov/growthcharts/.

Length: Length is measured in children too young to stand; height is measured once the child can stand. In general, length in normal term infants increases about 30% by 5 mo and > 50% by 12 mo; infants grow 25 cm during the 1st yr; and height at 5 yr is about double birth length. In boys, ½ the adult height is attained by about age 2; in girls, height at 19 mo is about ½ the adult height.

Rate of change in height (height velocity) is a more sensitive measure of growth than time-specific height measures. In general, healthy term infants and children grow about 2.5 cm/mo between birth and 6 mo, 1.3 cm/mo from 7 to 12 mo, and about 7.6 cm/yr between 12 mo and 10 yr. Before 12 mo, height velocity varies and is due in part to perinatal factors (eg, prematurity). After 12 mo, height is mostly genetically determined, and height velocity stays constant until puberty; a child's height relative to peers tends to remain the same. Some small-for-gestational-age infants tend to be shorter throughout life than infants whose size is appropriate for their gestational age. Boys and girls demonstrate little difference in height and growth rate during infancy and childhood.

Extremities grow faster than the trunk, leading to a gradual change in relative proportions; the crown-to-pubis/pubis-to-heel ratio is 1.7 at birth, 1.5 at 12 mo, 1.2 at 5 yr, and 1.0 after 7 yr.

Peak height velocity is reached at 12.1 ± 0.9 yr in girls and at 14.1 ± 0.9 yr in boys. A growth spurt in boys occurs between ages 13 and 15 ½; a gain of > 10 cm can be expected in the year of peak velocity. A growth spurt in girls begins at about age 11, may reach 4 cm in the year of peak velocity, and is almost completed by age 13 ½. If puberty is delayed (see Endocrine Disorders in Children: Delayed Puberty), growth in height may slow considerably. If the delay is not pathologic, the adolescent growth spurt occurs later and growth catches up, with height crossing percentile lines until the child reaches a genetically determined stature. At age 18, almost 2.54 cm of growth remains for boys and slightly less for girls, for whom growth is 99% complete. In girls with true precocious puberty (prior to age 6 ¹⁄₂), an early growth spurt occurs along with menarche at a young age and, ultimately, short stature because of early closure of growth plates.

Weight: Weight follows a similar pattern. Normal term neonates generally lose 5 to 8% of birth weight in the days after delivery but regain their birth weight within 2 wk. They then gain 14 to 28 g/day until 3 mo, then 4000 g between 3 and 12 mo, doubling their birth weight by 5 mo, tripling it by 12 mo, and almost quadrupling it by 2 yr. Between age 2 yr and puberty, weight increases 2 kg/yr. The recent epidemic of childhood obesity has involved markedly greater weight gain, even among very young children. In general, boys are heavier and taller than girls when growth is complete because boys have a longer prepubertal growth period, increased peak velocity during the pubertal growth spurt, and a longer adolescent growth spurt.

Head circumference: Head circumference reflects brain size and is routinely measured up to 2 yr. At birth, the brain is 25% of adult size, and head circumference averages 35 cm. Head circumference increases an average 1 cm/mo during the 1st year; growth is more rapid in the first 8 mo, and by 12 mo, the brain has completed ½ its postnatal growth and is 75% of adult size. Head circumference increases 3.5 cm over the next 2 yr; by age 3 yr, the brain is 80% of adult size, 90% by age 7 yr.

Body composition: Body composition (proportions of body fat and water) changes and affects volume of distribution of drugs (see Principles of Drug Treatment in Children: Distribution). Proportion of fat increases rapidly from 13% at birth to 20 to 25% by 12 mo, accounting for the chubby appearance of most infants. Subsequently, a slow fall occurs until preadolescence, when body fat returns to about 13%. There is a slow rise again until the onset of puberty, when body fat may again fall, especially in boys. After puberty, the percentage generally stays stable in girls, while in boys there tends to be a slight decline.

Body water measured as a percentage of body weight is 70% at birth, dropping to 61% at 12 mo (about equal to the adult percentage). This change is fundamentally due to a decrease in ECF from 45% to 28% of body weight. ICF stays relatively constant. After age 12 mo, there is a slow and variable fall in ECF and rise in ICF to adult levels of about 20% and 40%, respectively. The relatively larger amount of body water, its high turnover rate, and the comparatively high surface losses (due to a proportionately large surface area) make infants more susceptible to fluid deprivation than older children and adults.

Tooth eruption: Tooth eruption is variable (see Table 1: Physical Growth and Development: Tooth Eruption Times), primarily because of genetic factors. On average, normal infants should have 6 teeth by 12 mo, 12 teeth by 18 mo, 16 teeth by 2 yr, and all teeth (20) by 2½ yr; deciduous teeth are replaced by permanent teeth between the ages of 5 and 13 yr. Eruption of deciduous teeth is similar in both sexes; permanent teeth tend to appear earlier in girls. Tooth eruption may be delayed by familial patterns or by conditions such as rickets, hypopituitarism, hypothyroidism, or Down syndrome. Supernumerary teeth and congenital absence of teeth are probably normal variants.

Table 1
Tooth Eruption Times Teeth No. Age at Eruption* Deciduous (20 total) Lower central incisors 2 5–9 mo Upper central incisors 2 8–12 mo Upper lateral incisors 2 10–12 mo Lower lateral incisors 2 12–15 mo 1st molars† 4 10–16 mo Canines 4 16–20 mo 2nd molars† 4 20–30 mo Permanent (32 total) 1st molars† 4 5–7 yr Incisors 8 6–8 yr Bicuspids 8 9–12 yr Canines 4 10–13 yr 2nd molars† 4 11–13 yr 3rd molars† 4 17–25 yr *Varies greatly. † Molars are numbered from the front to the back of the mouth (see Fig. 1: Approach to Dental and Oral Symptoms: Identifying the teeth.).

Last full review/revision November 2005

Content last modified November 2005