NEUROMUSCULAR SYSTEM Term SGA infants have been described as hav-

ing the same developmental characteristics as their AGA counterparts (110, 111). In con- trast, distinct central and peripheral neurode- velopmental milestones have been described in pre-term infants. Taste develops at 12–15 weeks gestation, smell at about 20 weeks, and hearing begins at approximately 20–24 weeks. Prior to 28 weeks of gestation it is difficult to identify periods of wakefulness. Persistent stimuli lead to eye opening and closing for time periods measured principally in seconds (112, 113). At approximately 28 weeks gestation, however, there is a distinct change in the level of alertness (112, 114). At that time a gen- tle shake will arouse the infant from apparent sleep and will result in wakefulness for several minutes. Spontaneous alerting also occasion- ally occurs at this age. By 32 weeks, stimula- tion is no longer necessary. The eyes are often open and spontaneous roving eye movements appear (112, 113). By 36 weeks increased alertness can be observed readily and vigorous cry- ing appears during wakefulness. By term, the infant exhibits distinct periods of attention to visual and auditory stimuli (112, 113, 115).

The early components of sucking appear to occur in fetuses at about 7–8 weeks gestational age (110, 116, 117). At 8 weeks gestation the fetus will respond to touch around the mouth area. Swallowing is present at around 11–16 weeks and sucking appears at 18–24 weeks (116–118). The gag reflex is evident at 25–27 weeks although organized oesophageal activity does not develop until about 32 weeks ges- The early components of sucking appear to occur in fetuses at about 7–8 weeks gestational age (110, 116, 117). At 8 weeks gestation the fetus will respond to touch around the mouth area. Swallowing is present at around 11–16 weeks and sucking appears at 18–24 weeks (116–118). The gag reflex is evident at 25–27 weeks although organized oesophageal activity does not develop until about 32 weeks ges-

type of feed (126). These surges are even more tion, pre-term infants are also mature enough

marked in pre-term than term infants and occur to coordinate a swallow and breathe pattern.

even when nutritionally insignificant volumes The normal infant is then able to maintain a

of less than 1 ml/kg/day are fed. Absorptive concerted synchronous action for productive

capacity is also thought to increase rapidly on oral feeding (116–118).

feeding (126, 127). Premature babies, particu- By 32–34 weeks the infant should be able

larly those with birth weights <1100 g, are at to attach, suck and extend the tongue appro-

risk of glucose intolerance (128). Two proposed priately and begin breastfeeding. As long as

mechanisms include inappropriate secretion of the baby is able to keep the breast tissue in the

insulin by the pancreas and decreased sensitiv- mouth the infant’s peristaltic tongue move-

ity of the liver to the gluco-regulatory effect of ment can remove milk from the lactiferous

insulin (129). Alpha-glucosidases and lactase sinuses within the area of the areola (116, 118,

are both required to digest lactose. The activ- 119). The rooting reflex (the response shown

ity of alpha-glucosidases in the fetus reaches by a baby after the side of the cheek is touched

at least 70% of the activity in adults at a ges- – the infant turning to the breast with the

tational age of about 26–34 weeks, whereas mouth wide open) occurs around this time.

lactase activity at that gestational age is only Maturation continues and coordinated and

30% of adult activity (130, 131). Although effective use of the suck, swallow and breath-

theoretically lactose digestion should be lim- ing reflexes for nutritive purposes is achieved

ited, there is no evidence of clinical intolerance fully by 35–37 weeks gestation (116, 120).

among LBW infants. Pancreatic lipase secre- The infant is developmentally ready for

tion and bile salt concentrations are also low in complementary feeding from 4 months of cor-

comparison with the levels at term, but lingual rected age. Phasic biting disappears between 3

and gastric lipases are detectable in the fetus and 4 months and rooting diminishes between

from 26 weeks gestation and can assist in gas-

5 and 6 months. Stability of the trunk also

tric lipolysis (131, 132).

improves at this time and the infant begins to

be able to sit unsupported. Finger coordina-

GASTROINTESTINAL SYSTEM

tion develops by 6–7 months of age to permit The gastrointestinal tract is anatomically com- finger-feeding. By 12 months of age, rotary

plete at 24 weeks gestation but is functionally chewing is well established with controlled,

immature in both propulsive and absorptive sustained biting, and most infants are capable

capacity. Gastric emptying is slower in pre- of spoon-feeding themselves (110, 121).

term than term infants and fasting antral pres- sure is significantly reduced (133, 134). Fetal

ENDOCRINE AND EXOCRINE

small bowel transit appears at 28 weeks gesta-

SYSTEMS

tion but peristalsis is poorly organized. Motor Rate-limiting enzymes for gluconeogenesis

activity in the gastrointestinal tract is random develop late in gestation (122). Gluconeogen-

up to about 30 weeks gestational age. Over the esis is triggered hormonally after birth, but this

next 5–6 weeks it becomes clustered phasic process is ineffective at meeting the glucose

and then prolonged phasic. Migrating motor needs for cerebral metabolism (123). Achieving

complexes appear near term (135). Combined glucose homeostasis in the newborn infant is

with high lower oesophageal sphincter pres- dependent on exogenous sources. Enteral feed-

sures, this immaturity may predispose the ing induces the gut endocrine response, which

immature infant to gastro-oesophageal reflux mediates many metabolic and gastrointestinal

and result in feeding intolerance (136–139). adaptive changes (124, 125). Basal and post-

Large enteral intakes may also not be tolerated. prandial plasma concentrations of several hor-

Gastric capacity is also limited in LBW infants mones (especially enteroglucagon, gastrin and

and gastric distension may interfere with pul-

NEUROMUSCULAR SYSTEM Term SGA infants have been described as hav-