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Infant Growth and Development

Michael A. Davis, MD


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 a cloth.

The next skill in this sequence is the ability to locate an object under double layers (eg, a cube is placed under a cup and then the cup is covered with a cloth).

This is followed by the ability to locate an object after serial displacements (an object is hidden under one cover and then changed to another one). The younger infant always will look for it under the first cover, even though the position change was seen. Later, he will become successful with this task, as long as each successive displacement is observed. At the end of the second year, the child is able to deduce the location of an object that is hidden without observing the displacement.

Causality. Initially, the infant accidentally discovers that his actions produce a certain effect (eg, kicking the side of the crib activates a mobile overhead). The infant learns that actions cause consistent effects.

Language Development

Delays in language development are more common than delays in other developmental domains.

Between 10 and 18 months of age, word counts help in assessing a child's expressive skills; after 18 months of age, vocabularies increase exponentially, and the number of words an infant knows should exceed the ability of the parent to count them.

Receptive language skills reflect the ability to understand language. Expressive language skills reflect the ability to make thoughts, ideas, and desires known to others.

Language development during infancy can be divided into three periods: prespeech, naming, and word combination periods.

Prespeech Period (0 to 10 months). Receptive language is characterized by an increasing ability to localize sounds, such as a bell. Expressive language consists of cooing. At about 3 months, the infant will begin vocalizing after hearing an adult speak.

At 6 months of age, the infant adds consonants to the vowel sounds in a repetitive fashion (babbling). When a random vocalization (eg, "dada") is interpreted by the parents as a real word, the parent will show pleasure and joy. In so doing, parents reinforce the repeated use of these sounds.

Naming Period (10 to 18 months). The infant's realizes that people have names and objects have labels. The infant begins to use the words "dada" and "mama" appropriately. Infants next recognize and understand their own names and the meaning of "no." By 12 months of age, some infants understand as many as 100 words. They can follow a simple command as long as the speaker uses a gesture. Early in the second year, a gesture no longer is needed. Expressive language progresses at a somewhat slower rate. The infant will say at least one "real" word (ie, other than mama, dada) before his first birthday. At this time, the infant also will begin to verbalize with sentence-like intonation and rhythm (immature jargoning). As expressive vocabulary increases, real words are added (mature jargoning). By the end of the naming period, the infant will use about 25 words.

Word Combination Period (18 to 24 months). Children begin to combine words 6 to 8 months after they say their first word.

Early word combinations are "telegraphic" in that they do not contain prepositions, pronouns, and articles (eg, "Go out"). A stranger should be able to understand at least 50% of the infant’s speech.

Red Flags in Cognitive Development

Language development provides an estimate of verbal intelligence; problem-solving provides an estimate of nonverbal intelligence. If deficiencies are global (ie, skills are delayed in both domains), there is a possibility of mental retardation. Mental retardation refers to significant sub-average general intellectual functioning as measured by standardized tests.

When a discrepancy exists between problem-solving and language abilities, with only language being deficient, the possibility of a hearing impairment or a communication disorder should be excluded.

If either language or problem-solving skills is deficient, the child is at high risk for a learning disability later.

All children who have delayed language development should receive audiologic testing to rule out hearing loss. Deaf infants will begin to babble on time at 6 months, but these vocalizations will gradually decline thereafter.

Psychosocial Development

Emotional Development. Emotions are present in infancy and motivate expression (pain elicits crying).

Emotions are mediated through the limbic system, which is responsible for processing emotion-producing stimuli and then initiating emotional responses.

Social Development

Social milestones begin with bonding, which reflects the feeling of the caregiver for the child. Attachment represents the feeling of the infant for the caregiver, and it develops within a few months.

When recognition of and attachment to a caregiver develops, the simple sight of this person will elicit a smile. The infant becomes more discriminating in producing a smile as he begins to differentiate between familiar and unfamiliar faces. The infant learns to use smiling to manipulate the environment and satisfy personal needs.

Temperament represents the style of a child's emotional and behavioral response in a variety of situations. It is determined by genetic factors but is modified by environmental forces.

Adaptive Skill Development

Adaptive skills consist of the skills required for independence in feeding, dressing, toileting, and other activities of daily living. Development of adaptive skill is influenced by the infant's social environment, and by motor and cognitive skill attainment.

An infant may demonstrate delays in adaptive skills when social support and encouragement are lacking.

Red Flags in Psychosocial Development

Colic may be an early indication of a "difficult" temperament.

Delay in the appearance of a smile suggests an attachment problem, which may be associated with maternal depression. In severe cases, child neglect or abuse may be suspected. A delay in smiling also may be caused by visual or cognitive impairment.

Failure to develop social relationships suggests autism when it is accompanied by delayed or deviant language development and stereotypic behaviors.

Delays in adaptive skills may indicate overprotective parents or an excessive emphasis on cleanliness or orderliness. §