Infant growth and development.

“Infant” is derived from the Latin word, “infans,” meaning “unable to speak.” Thus, many define infancy as the period from birth to approximately 2 years of age, when language begins to flourish. It is an exciting period of “firsts”—first smile, first successful grasp, first evidence of separation anxiety, first word, first step, first sentence. The infant is a dynamic, ever-changing being who undergoes an orderly and predictable sequence of neurodevelopmental and physical growth. This sequence is influenced continuously by intrinsic and extrinsic forces that produce individual variation and make each infant’s developmental path unique. Intrinsic influences include the child’s physical characteristics, state of wellness or illness, temperament, and other genetically determined attributes. Extrinsic influences during infancy originate primarily from the family: the personalities and style of caregiving by parents and siblings, the family’s economic status with its impact on resources of time and money, and the cultural milieu into which the infant is born. Neurodevelopmental sequences can be viewed broadly in terms of the traditional developmental milestones. Developmental milestones provide a systematic approach by which to observe the progress of the infant over time. Attainment of a particular skill builds on the achievement of earlier skills; only rarely are skills skipped. When this happens, the advanced skill may represent a “splinter” skill, that is, a deviant developmental pattern. For example, five-word sentences in a 2-year-old child who does not follow simple commands may represent echolalia typical of autism. The sentences are not meaningful and have no communicative intent. Delays in one developmental domain may impair development in another domain. For example, immobility due to neuromuscular disorders prevents exploration of the environment and, in turn, impedes cognitive development arising through manipulation of objects. Last, a deficit in one domain may compromise the assessment of skill levels in another domain, even though development in the second domain is normal. For example, it is difficult to assess problemsolving skills in a child who has cerebral palsy because the child may understand the concept of matching geometric forms, yet be unable to insert them physically into a formboard. Developmental milestones serve as the basis of most standardized assessment and screening tools. Although these screening tools provide the clinician with a structured method of observing the infant’s progress and help define a developmental delay, many lack sensitivity. Parental concern in the face of normal results in developmental screening should not be disregarded. Focusing narrowly on discrete milestones may fail to reveal atypical organizational processes that are involved in the child’s developmental progress. Thus, it is important to analyze all milestones within the context of the child’s history, growth, and physical examination as part of an ongoing surveillance program. Only then is it possible to formulate an overall impression of the child’s true developmental status and the need for intervention. Although milestones form the foundation of the discussion, the primary intent of this article is to provide broader insights into infant developmental processes and to help the clinician recognize warning behaviors (“red flags”) indicative ARTICLE