Physical Development

A newborn’s weight may initially decrease 10% below birthweight in the 1st wk as a result of excretion of excess extravascular fluid and limited nutritional intake. Nutrition improves as colostrum is replaced by higher-fat breast milk, as infants learn to latch on and suck more efficiently, and as mothers become more comfortable with feeding techniques. Infants regain or exceed birthweight by 2 wk of age and should grow at approximately 30 g (1 oz)/day during the 1st mo (see Table 13-1). This is the period of fastest postnatal growth. Limb movements consist largely of uncontrolled writhing, with apparently purposeless opening and closing of the hands. Smiling occurs involuntarily. Eye gaze, head turning, and sucking are under better control and thus can be used to demonstrate infant perception and cognition. An infant’s preferential turning toward the mother’s voice is evidence of recognition memory.

Six behavioral states have been described (Chapter 7). Initially, sleep and wakefulness are evenly distributed throughout the 24-hr day (Fig. 8-1). Neurologic maturation accounts for the consolidation of sleep into blocks of 5 or 6 hr at night, with brief awake, feeding periods. Learning also occurs; infants whose parents are consistently more interactive and stimulating during the day learn to concentrate their sleeping during the night.

Figure 8-1 Typical sleep requirements in children.

(From Ferber R: Solve your child’s sleep problems, New York, 1985, Simon & Schuster.)

Cognitive Development

Infants can differentiate among patterns, colors, and consonants. They can recognize facial expressions (smiles) as similar, even when they appear on different faces. They also can match abstract properties of stimuli, such as contour, intensity, or temporal pattern, across sensory modalities. Infants at 2 mo of age can discriminate rhythmic patterns in native vs non-native language. Infants appear to seek stimuli actively, as though satisfying an innate need to make sense of the world. These phenomena point to the integration of sensory inputs in the central nervous system. Caretaking activities provide visual, tactile, olfactory, and auditory stimuli; all of these support the development of cognition. Infants habituate to the familiar, attending less to repeated stimuli and increasing their attention to novel stimuli.

Emotional Development

The infant is dependent on the environment to meet his or her needs. The consistent availability of a trusted adult to meet the infant’s urgent needs creates the conditions for secure attachment. Basic trust vs mistrust, the first of Erikson’s psychosocial stages (Chapter 6), depends on attachment and reciprocal maternal bonding. Crying occurs in response to stimuli that may be obvious (a soiled diaper), but are often obscure. Infants who are consistently picked up and held in response to distress cry less at 1 yr and show less aggressive behavior at 2 yr. Cross-cultural studies show that in societies in which infants are carried close to the mother, babies cry less than in societies in which babies are only periodically carried. Crying normally peaks at about 6 wk of age, when healthy infants may cry up to 3 hr/day, then decreases to 1 hr or less by 3 mo.

The emotional significance of any experience depends on both the individual child’s temperament and the parent’s responses (see Table 6-1); differing feeding schedules produce differing reactions. Hunger generates increasing tension; as the urgency peaks, the infant cries, the parent offers the breast or bottle and the tension dissipates. Infants fed “on demand” consistently experience this link between their distress, the arrival of the parent, and relief from hunger. Most infants fed on a fixed schedule quickly adapt their hunger cycle to the schedule. Those who cannot because they are temperamentally prone to irregular biologic rhythms experience periods of unrelieved hunger as well as unwanted feedings when they already feel full. Similarly, infants who are fed at the parents’ convenience, with neither attention to the infant’s hunger cues nor a fixed schedule may not consistently experience feeding as the pleasurable reduction of tension. These infants often show increased irritability and physiologic instability (spitting, diarrhea, poor weight gain) as well as later behavioral problems.

Implications for Parents and Pediatricians

Success or failure in establishing feeding and sleep cycles determines parents’ feelings of efficacy. When things go well, the parents’ anxiety and ambivalence, as well as the exhaustion of the early weeks, decrease. Infant issues (colic) or familial conflict will prevent this from occurring. With physical recovery from delivery and endocrinologic normalization, the mild postpartum depression that affects many mothers passes. If the mother continues to feel sad, overwhelmed, and anxious, the possibility of moderate to severe postpartum depression, found in 10% of postpartum women, needs to be considered. Major depression that arises during pregnancy or in the postpartum period threatens the mother-child relationship and is a risk factor for later cognitive and behavioral problems. The pediatrician may be the first professional to encounter the depressed mother and should be instrumental in assisting her in seeking treatment (Chapter 7).

Physical Development

Between 3 and 4 mo of age, the rate of growth slows to approximately 20 g/day (see Table 13-1; see Figs. 9-1 and 9-2 on the Nelson Textbook of Pediatrics website at www.expertconsult.com). By 4 mo, birthweight is doubled. Early reflexes that limited voluntary movement recede. Disappearance of the asymmetric tonic neck reflex means that infants can begin to examine objects in the midline and manipulate them with both hands (Chapter 584). Waning of the early grasp reflex allows infants both to hold objects and to let them go voluntarily. A novel object may elicit purposeful, although inefficient, reaching. The quality of spontaneous movements also changes, from larger writhing to smaller, circular movements that have been described as “fidgety.” Abnormal or absent fidgety movements may constitute a risk factor for later neurologic abnormalities.

Increasing control of truncal flexion makes intentional rolling possible. Once infants can hold their heads steady while sitting, they can gaze across at things rather than merely looking up at them, and can begin taking food from a spoon. At the same time, maturation of the visual system allows greater depth perception.

In this period, infants achieve stable state regulation and regular sleep-wake cycles. Total sleep requirements are approximately 14-16 hr/24 hr, with about 9-10 hr concentrated at night and 2 naps/day. About 70% of infants sleep for a 6-8 hr stretch by age 6 mo (see Fig. 8-1). By 4-6 mo, the sleep electroencephalogram shows a mature pattern, with demarcation of rapid eye movement (REM) and 4 stages of non-REM sleep. The sleep cycle remains shorter than in adults (50-60 min vs approximately 90 min). As a result, infants arouse to light sleep or wake frequently during the night, setting the stage for behavioral sleep problems (Chapter 17).

Cognitive Development

The overall effect of these developments is a qualitative change. At 4 mo of age, infants are described as “hatching” socially, becoming interested in a wider world. During feeding, infants no longer focus exclusively on the mother, but become distracted. In the mother’s arms, the infant may literally turn around, preferring to face outward.

Infants at this age also explore their own bodies, staring intently at their hands, vocalizing, blowing bubbles, and touching their ears, cheeks, and genitals. These explorations represent an early stage in the understanding of cause and effect as infants learn that voluntary muscle movements generate predictable tactile and visual sensations. They also have a role in the emergence of a sense of self, separate from the mother. This is the first stage of personality development. Infants come to associate certain sensations through frequent repetition. The proprioceptive feeling of holding up the hand and wiggling the fingers always accompanies the sight of the fingers moving. Such self sensations are consistently linked and reproducible at will. In contrast, sensations that are associated with “other” occur with less regularity and in varying combinations. The sound, smell, and feel of the mother sometimes appear promptly in response to crying, but sometimes do not. The satisfaction that the mother or another loving adult provides continues the process of attachment.

Emotional Development and Communication

Babies interact with increasing sophistication and range. The primary emotions of anger, joy, interest, fear, disgust, and surprise appear in appropriate contexts as distinct facial expressions. When face-to-face, the infant and a trusted adult can match affective expressions (smiling or surprise) about 30% of the time. Initiating games (facial imitation, singing, hand games) increases social development. Such face-to-face behavior reveals the infant’s ability to share emotional states, the first step in the development of communication. Infants of depressed parents show a different pattern, spending less time in coordinated movement with their parents and making fewer efforts to re-engage. Rather than anger, they show sadness and a loss of energy when the parents continue to be unavailable.

Implications for Parents and Pediatricians

Motor and sensory maturation makes infants at 3-6 mo exciting and interactive. Some parents experience their 4 mo old child’s outward turning as a rejection, secretly fearing that their infants no longer love them. For most parents, this is a happy period. Most parents excitedly report that they can hold conversations with their infants, taking turns vocalizing and listening. Pediatricians share in the enjoyment, as the baby coos, makes eye contact, and moves rhythmically. If this visit does not feel joyful and relaxed, causes such as social stress, family dysfunction, parental mental illness, or problems in the infant-parent relationship should be considered. Parents can be reassured that responding to an infant’s emotional needs cannot spoil him or her. Giving vaccines and drawing blood while the child is seated on the parent’s lap or nursing at the breast increases pain tolerance.

Physical Development

Growth slows more (see Table 13-1; see Figs. 9-1 and 9-2 on the Nelson Textbook of Pediatrics website at www.expertconsult.com). By the 1st birthday, birthweight has tripled, length has increased by 50%, and head circumference has increased by 10 cm. The ability to sit unsupported (6-7 mo) and to pivot while sitting (around 9-10 mo) provides increasing opportunities to manipulate several objects at a time and to experiment with novel combinations of objects. These explorations are aided by the emergence of a thumb-finger grasp (8-9 mo) and a neat pincer grasp by 12 mo. Many infants begin crawling and pulling to stand around 8 mo, followed by cruising. Some walk by 1 yr. Motor achievements correlate with increasing myelinization and cerebellar growth. These gross motor skills expand infants’ exploratory range and create new physical dangers as well as opportunities for learning. Tooth eruption occurs, usually starting with the mandibular central incisors. Tooth development reflects skeletal maturation and bone age, although there is wide individual variation (see Table 8-3 and Chapter 299).

Cognitive Development

The 6 mo old infant has discovered his hands and will soon learn to manipulate objects. At first, everything goes into the mouth. In time, novel objects are picked up, inspected, passed from hand to hand, banged, dropped, and then mouthed. Each action represents a nonverbal idea about what things are for (in Piagetian terms, a schema; Chapter 6). The complexity of an infant’s play, how many different schemata are brought to bear, is a useful index of cognitive development at this age. The pleasure, persistence, and energy with which infants tackle these challenges suggest the existence of an intrinsic drive or mastery motivation. Mastery behavior occurs when infants feel secure; those with less secure attachments show limited experimentation and less competence.

A major milestone is the achievement at about 9 mo of object permanence (constancy), the understanding that objects continue to exist, even when not seen. At 4-7 mo of age, infants look down for a yarn ball that has been dropped but quickly give up if it is not seen. With object constancy, infants persist in searching. They will find objects hidden under a cloth or behind the examiner’s back. Peek-a-boo brings unlimited pleasure as the child magically brings back the other player. Events seem to occur as a result of the child’s own activities.

Emotional Development

The advent of object permanence corresponds with qualitative changes in social and communicative development. Infants look back and forth between an approaching stranger and a parent, and may cling or cry anxiously, demonstrating stranger anxiety. Separations often become more difficult. Infants who have been sleeping through the night for months begin to awaken regularly and cry, as though remembering that the parents are in the next room.

A new demand for autonomy also emerges. Poor weight gain at this age often reflects a struggle between an infant’s emerging independence and parent’s control of the feeding situation. Use of the 2-spoon method of feeding (1 for the child and 1 for the parent), finger foods, and a high chair with a tray table can avert potential problems. Tantrums make their first appearance as the drives for autonomy and mastery come in conflict with parental controls and the infants’ still-limited abilities.

Communication

Infants at 7 mo of age are adept at nonverbal communication, expressing a range of emotions and responding to vocal tone and facial expressions. Around 9 mo of age, infants become aware that emotions can be shared between people; they show parents toys as a way of sharing their happy feelings. Between 8 and 10 mo of age, babbling takes on a new complexity, with many syllables (“ba-da-ma”) and inflections that mimic the native language. Infants now lose the ability to distinguish between vocal sounds that are undifferentiated in their native language. Social interaction (attentive adults taking turns vocalizing with the infant) profoundly influences the acquisition and production of new sounds. The first true word (i.e., a sound used consistently to refer to a specific object or person) appears in concert with an infant’s discovery of object permanence. Picture books now provide an ideal context for verbal language acquisition. With a familiar book as a shared focus of attention, a parent and child engage in repeated cycles of pointing and labeling, with elaboration and feedback by the parent.

Implications for Parents and Pediatricians

With the developmental reorganization that occurs around 9 mo of age, previously resolved issues of feeding and sleeping re-emerge. Pediatricians can prepare parents at the 6 mo visit so that these problems can be understood as the result of developmental progress and not regression. Parents should be encouraged to plan ahead for necessary, and inevitable, separations (e.g., baby sitter, daycare). Routine preparations may make these separations easier. Introduction of a transitional object may allow the infant to self-comfort in the parents’ absence. The object cannot have any potential for asphyxiation or strangulation.

Infants’ wariness of strangers often makes the 9 mo examination difficult, particularly if the infant is temperamentally prone to react negatively to unfamiliar situations. Initially, the pediatrician should avoid direct eye contact with the child. Time spent talking with the parent and introducing the child to a small, washable toy will be rewarded with more cooperation. The examination can be continued on the parent’s lap when feasible.