Infancy 2002. Growth in infancy Physiology of infancy GI Renal Development of feeding skills Nutrient requirements Infant formulas Non milk feedings/solids Oral health. GROWTH IN FIRST 12 MONTHS.
Growth in infancy • Physiology of infancy • GI • Renal • Development of feeding skills • Nutrient requirements • Infant formulas • Non milk feedings/solids • Oral health
GROWTH IN FIRST 12 MONTHS • From birth to 1 year of age, normal human infants triple their weight and increase their length by 50%. • Growth in the first 4 months of life is the fastest of the whole lifespan - birthweight usually doubles by 4 months • 4-8 months is a time of transition to slower growth • By 8 months growth patterns more like those of 2 year old than those of newborn.
Weight Gain in Grams per Day in One Month Increments - Girls Guo et al., J Peds. 1991
Weight Gain in Grams per Day in One Month Increments - Boys Guo et al., J Peds. 1991
Energy & Protein • Young infant requires substantial percentage of energy intake for growth • Relatively large percentage of requirement for protein in young infant is accounted for by protein accretion
Body Composition • BMI and percentage of body weight made up of fat increase rapidly during the first months of life • Fat accounts for 0.5% of body weight at the fifth month of fetal growth and 16% at term. • After birth, fat accumulates rapidly until approximately 9 months of age
Individual Growth Patterns • Weight and length at term appear to be primarily determined by nongenetic maternal factors • Birth weigh and birth length weakly correlate with subsequent weight and length values
Individual Growth Patterns, cont. • Extremes of birth weight and length tend to regress to the mean, and genetic factors appear to have a stronger effect by the middle of the first year. • infants who are born small but are genetically destined to be longer may shift percentiles on growth grids during the first 3 to 6 months • larger infants at birth whose genotypes are for smaller size tend to grow at their fetal rates for several months before the lag-down in growth becomes evident
Individual Growth Patterns, cont. • African American males and females are smaller than Caucasians at birth, but they grow more rapidly during the first 2 years • Patterns of growth in breastfed infants may be different from formula fed infants
Assessment of Growth • Growth Charts • http://www.cdc.gov/growthcharts/ • Growth Velocity
New Growth Charts • Data from old charts came from private study of primarily Caucasian, formula-fed, middle-class infants from southwestern Ohio • New charts have data from NHANES and use more sophisticated smoothing techniques • 16 new charts provided by gender and age
New Growth Charts • Clinical charts for infancy for girls and boys: • weight • length • weight for length • OFC • Choice between outer limits at 3rd and 97th or 5th and 95th percentiles
In utero • fetal GI tract is exposed to constant passage of fluid that contains a range of physiologically active factors: • growth factors • hormones • enzymes • immunoglobulins • these play a role in mucosal differentiation and GI development as well as development of swallowing and intestinal motility
At Birth • gut of the newborn is faced with the formidable task of passing, digesting, and absorbing large quantities of intermittent boluses of milk • comparable feeds per body weight for adults would be 15 to 20 L
Enteral Feeding Requirements • Coordinated sucking and swallowing • Gastric emptying • Intestinal motility • Secretions: salivary, gastric, pancreatic, hepatobiliary • Enterocyte function in terms of enzyme synthesis, absorption, mucosal protection • Metabolism of products of digestion and absorption • Expulsion of undigested waste products
Human Milk • complements Immaturities of these systems as well as their maturation • Epithelial growth factors and hormones • Digestive enzymes - lipases and amylase
Motility - Upper GI • Esophageal motility is decreased in the newborn • LES is primarily above the diaphragm • LES pressure is less for first months • Gastric Emptying may be delayed
Motility - Intestinal • Intestinal motility is more disorganized • Prolonged transit time in upper intestines may improve absorption of nutrients • Rapid emptying of ileum and colon may reduce time for water and electrolyte absorption and increase risk of dehydration
Stooling • Gasrtro-colonic reflex is active in the neonate: entry of food into beginning of small intestine causes reflexive propulsion toward the rectum • Passage of stool occurs within 24 hours for most healthy full term infants. • Meconium is passed for the first 2 or 3 days
Stooling, cont. • In first week of life may pass as many as 9 stools per day, declines to 3 or 4 by second week • Later breast fed babies may not even have daily stools. • Fetal gut is sterile, but infant exposed to microorganisms during birth. • Bacteria may be detected in meconium within 4 hours of birth following vaginal birth
Effect of infant formula on stool characteristics of young infants. Pediatrics 1995 Jan;95(1):50-4 • 238 healthy 1-month-old infant were fed one of four commercial formula preparations (Enfamil, Enfamil with Iron, ProSobee, and Nutramigen) for 12 to 14 days in a prospective double-blinded (parent/physician) fashion. Parents completed a daily diary of stool characteristics as well as severity of spitting, gas, and crying for the last 7 days of the study period. A breast-fed infant group was studied as well.
Gut Hormones • Gastrointestinal peptides are found in venous cord blood at birth in levels similar to those of fasting adults • In fetal distress a number of gut peptides are elevated which might account for passage of meconium • With enteral feeding levels of gut hormones (motilin, neurotensin, GIP (gastric inhibitory peptide), gastrin, enteroglucagon, PP - pancreatic polypeptide, rise rapidly
Choice of breast or formula feeds Enteric intake (induces epithelia hyperplasia and stimulates production of microvillous enzymes) Early enteral feeding (enteral feeding is strongly encouraged to promote GI function and differentiation) Gut Hormones Influenced By:
Nutrient composition in early diet may have long term effects on GI function and metabolism Animal models show that glucose and amino acid transport activities are programmed by composition of early diet Animals weaned onto high CHO diet have higher rates of glucose absorption as adults compared to those weaned on high protein diet Programming by Early Diet
Pancreatic function is relatively deficient at birth and mature levels of pancreatic enzymes are not achieved until late infancy Pancreatic amylase activity increases after 4 to 6 monthsLipase levels do not approach adult efficiency until about 6 months Pancreas
LES tone increases after 6 months and is associated with less reflux in most infants Gastric acid and pepsin activity do not reach adult levels until 2 years Pancreatic amylase increases by 6 monthsRetention of lactase activity is typical until 3 to 5 years. Fat absorption does not approach adult efficiency until about 6 months Lipase reaches adult levels by 2 years. Maturation in First Year
Limited ability to concentrate urine in first year due to immaturities of nephron and pituitary Potential Renal solute load determined by nitrogenous end products of protein metabolism, sodium, potassium, phosphorus, and chloride. Renal
Most normal adults are able to achieve urine concentrations of 1300 to 1400 mOsm/l Healthy newborns may be able to concentrate to 900-1100 mOsm/l, but isotonic urine of 280-310 mOsm/l is the goal In most cases this is not a concern, but may become one if infant has fever, high environmental temperatures, or diarrhea Urine Concentrations
Water Needs • Water requirement is determined by: • water loss • evaporation through the skin and respiratory tract (insensible water loss) • perspiration when the environmental temperature is elevated • elimination in urine and feces. • water required for growth • solutes derived from the diet
Water, cont. • Water lost by evaporation in infancy and early childhood accounts for more than 60% of that needed to maintain homeostasis, as compared to 40% to 50% • NAS recommends 1.5 ml water per kcal in infancy.
Development of Infant Feeding Skills • Birth • tongue is disproportionately large in comparison with the lower jaw: fills the oral cavity • lower jaw is moved back relative to the upper jaw, which protrudes over the lower by approximately 2 mm. • tongue tip lies between the upper and lower jaws. • "fat pad" in each of the cheeks: serves as. It is thought that these pads serve as a prop for the muscles in the cheek, maintaining rigidity of the cheeks during suckling. • Feeding pattern described as “suckling”
Developmental Changes • Oral cavity enlarges and tongue fills up less • Tongue grows differentially at the tip and attains motility in the larger oral cavity. • Elongated tongue can be protruded to receive and pass solids between the gum pads and erupting teeth for mastication. • Mature feeding is characterized by separate movements of the lip, tongue, and gum pads or teeth