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Infant Growth and Development

Infancy consists of the period from birth to about two years of age. Developmental milestones provide a systematic method of observing the progress of the infant over time. Advances occur in physical growth, motor development, cognitive development, and psychosocial development.

Physical Growth Milestones

Fetal weight gain is greatest during the third trimester. Birth weight is regained by 2 weeks of age and doubles by 5 months. During the first few months of life, this rapid growth continues, after which the growth rate decelerates.

Height does not double until between 3 and 4 years of age.

Head growth during the first 5 or 6 months results from continued neuronal cell division. Later, increasing head size is the result of neuronal cell growth and supporting tissue proliferation.

Attainment of growth milestones will vary depending on each child's genetic and ethnic characteristics.

Average Physical Growth Parameters


Occipitofrontal Circumference





35.0 cm (13.8 in)

+2 cm/mo (0 to 3 mo)

+1 cm/mo (3 to 6 mo)

+0.5 cm/mo (6 to 12 mo)

Mean = 1 cm/mo

50.8 cm (20.0 in)

+25.4 cm


3.0 to 3.5 kg (6.6 to 7.7 lb)

Regains birthweight by 2 wk

Doubles birthweight by 5 mo

Central incisors--6 mo

Lateral incisors--8 mo

1 year

47.0 cm (18.5 in)

+2 cm

76.2 cm (30.0 in)

+12.7 cm

10.0 kg (22 lb)

Triples birthweight

First molars--14 mo

Canines--19 mo

2 years

49.0 cm (19.3 in)

88.9 cm (35.0 in)

12.0 to 12.5 kg (26.4 to 27.5 lb)

Quadruples birthweight

Second molars--24 mo


Red Flags in Physical Growth

Occipitofrontal Circumference

Microcephaly is associated with an increased incidence of mental retardation, but there is no direct relationship between small head size and decreased intelligence. Microcephaly associated with genetic or acquired disorders usually has cognitive implications.

Macrocephaly may be caused by hydrocephalus, which is associated with learning disabilities. Macrocephaly without hydrocephalus also is associated with a higher prevalence of cognitive deficits. It may be caused by metabolic or anatomic abnormalities. Fifty percent of cases of macrocephaly are familial and have no effect on intellect. When evaluating the infant with isolated macrocephaly, the finding of a large head size in one or both parents is reassuring.

Height and Weight

Although the majority of individuals who are of below- or above-average size are otherwise normal, there is an increased prevalence of developmental disabilities in these two groups.

Many genetic syndromes are associated with short stature; large stature syndromes are less common. When considering deviation from the norm, short stature in the family is reassuring.


Most isolated minor dysmorphic features are inconsequential; however, the presence of three or more indicative of developmental dysfunction.

Seventy-five percent of minor superficial dysmorphisms can be found by examining the face, skin, and hands.

Motor Development Milestones

Motor milestones are ascertained from the developmental history and observation. The developmental quotient (DQ) is the developmental age divided by chronologic age times 100. A quotient above 85 is considered within normal limits; a quotient below 70 is considered abnormal.

Gross motor development begins with prone milestones (holding head up, rolling) and progresses to sitting, and then standing and ambulating.

Fine Motor Development

In the first year of life, fine motor development is highlighted by the development of a pincer grasp. During the second year of life, the infant learns to use objects as tools during play.

Reaching becomes more accurate, and objects are initially brought to the mouth for oral exploration. As the pincer grasp and macular vision improve, precise manual exploration replaces oral exploration.

Red Flags in Motor Development

Persistent listing to one side at 3 months of age often is the earliest indication of neuromotor dysfunction.

Spontaneous frog-legs posturing suggests hypotonia/ weakness, and scissoring suggests spastic hypertonus. Early rolling (1 to 2 months), pulling directly to a stand at 4 months (instead of to a sit), W-sitting, bunny hopping, and persistent toe walking may indicate spasticity.

Hand dominance prior to 18 months of age should prompt the clinician to examine the contralateral upper extremity for weakness associated with a hemiparesis.

Cognitive Development Milestones

Intellectual development depends on learning, and it requires attention, information processing, and memory. Intellectual development is reflected in increased ability to comprehend, reason, and make judgments.

Language is the single best indicator of intellectual potential; problem-solving skills are the next best measure. Gross motor skills correlate least with cognitive potential; most infants with mental retardation walk on time.

Problem-solving Skills

As cognitive abilities continue to advance, the infant learns to shift attention between two objects (one in each hand), compare, make choices, and discard or combine objects.

The 1-year-old child recognizes objects and associates them with their functions. Thus, he begins to use them functionally as "tools" instead of mouthing, banging, and throwing them.

Midway through the second year, the child begins to label objects and actions and categorize them, allowing the child to match objects that are the same and later to match an object to its picture.

Object Permanence

Prior to the infant's mastery of object permanence, a person or object that is "out of sight" is "out of mind," and its disappearance does not evoke a reaction.

The child will show interest in peek-a-boo play, and separation anxiety will occur when a loved one leaves the room. Shortly thereafter, the child will begin to look for an object that has been dropped.

The child will progress to finding an object that has been hidden under a cloth. A more complex task is locating an object that has been wrapped inside.