Water, energy and early postnatal growth in preterm infants

Metabolic-endocrine disruption due to preterm birth impacts growth, body composition, and neonatal outcome

Despite optimized nutrition, preterm-born infants grow slowly and tend to over-accrete body fat. We hypothesize that the premature dissociation of the maternal-placental-fetal unit disrupts the maintenance of physiological endocrine function in the fetus, which has severe consequences for postnatal development. This review highlights the endocrine interactions of the maternal-placental-fetal unit and the early perinatal period in both preterm and term infants. We report on hormonal levels (including tissue, thyroid, adrenal, pancreatic, pituitary, and placental hormones) and nutritional supply and their impact on infant body composition. The data suggest that the premature dissociation of the maternal-placental-fetal unit leads to a clinical picture similar to panhypopituitarism. Further, we describe how the premature withdrawal of the maternal-placental unit, neonatal morbidities, and perinatal stress can cause differences in the levels of growth-promoting hormones, particularly insulin-like growth factors (IGF). In combination with the endocrine disruption that occurs following dissociation of the maternal-placental-fetal unit, the premature adaptation to the extrauterine environment leads to early and fast accretion of fat mass in an immature body. In addition, we report on interventional studies that have aimed to compensate for hormonal deficiencies in infants born preterm through IGF therapy, resulting in improved neonatal morbidity and growth. IMPACT: Preterm birth prematurely dissociates the maternal-placental-fetal unit and disrupts the metabolic-endocrine maintenance of the immature fetus with serious consequences for growth, body composition, and neonatal outcomes. The preterm metabolic-endocrine disruption induces symptoms resembling anterior pituitary failure (panhypopituitarism) with low levels of IGF-1, excessive postnatal fat mass accretion, poor longitudinal growth, and failure to thrive. Appropriate gestational age-adapted nutrition alone seems insufficient for the achievement of optimal growth of preterm infants. Preliminary results from interventional studies show promising effects of early IGF-1 supplementation on postnatal development and neonatal outcomes.

Protein use and weight-gain quality in very-low-birth-weight preterm infants fed human milk or formula

Background

Nutritional management of preterm infants aims to approximate the tissue growth and body composition of a fetus of the same postmenstrual age. The adequacy of the quality of protein supply can influence the rate and the relative quality of weight gain.

Objective

We investigated the protein balance according to feeding regimen and the association between human milk feeding and fat-free mass content at the term-corrected age in very-low-birth-weight preterm infants.

Design

A prospective observational study was conducted. Inclusion criteria were as follows: healthy infants, gestational age ≤32 wk, birth weight <1500 g, stable clinical conditions, and feeding by mouth with human milk or formula at discharge. Infants were enrolled at hospital discharge. At enrollment, macronutrient intakes and protein balance were determined. Anthropometric measurements and body composition were also assessed. The nutritional composition of human milk was calculated by infrared spectroscopy. The protein balance was determined according to the nitrogen balance standard method. Body composition was assessed by an air-displacement plethysmography system. At the term-corrected age, anthropometry and body composition assessments were repeated.

Results

Seventeen preterm infants fed fortified human milk and 15 preterm infants fed formula were enrolled. At discharge, despite similar macronutrient intakes, infants fed fortified human milk showed a higher nitrogen balance (expressed as mg · kg-1 · d-1) compared with preterm formula-fed infants (mean ± SD: 488.3 ± 75 compared with 409.8 ± 85 mg · kg-1 · d-1, P = 0.009). At term-corrected age, growth was similar in the 2 groups, whereas fortified human milk-fed infants showed a higher percentage of fat-free mass (85.1% ± 2.8% compared with 80.8% ± 3.2%, P = 0.002). Moreover, at multiple linear regression, fat-free mass content was independently associated with being fed human milk (R2 = 0.93, P < 0.0001).

Conclusion

Our findings suggest that human milk feeding is associated with early fat-free mass deposition in healthy and stable preterm infants. This trial was registered at www.clinicaltrials.gov as NCT03013374.

Does Human Milk Modulate Body Composition in Late Preterm Infants at Term-Corrected Age?

(1) Background: Late preterm infants account for the majority of preterm births and are at risk of altered body composition. Because body composition modulates later health outcomes and human milk is recommended as the normal method for infant feeding, we sought to investigate whether human milk feeding in early life can modulate body composition development in late preterm infants; (2) Methods: Neonatal, anthropometric and feeding data of 284 late preterm infants were collected. Body composition was evaluated at term-corrected age by air displacement plethysmography. The effect of human milk feeding on fat-free mass and fat mass content was evaluated using multiple linear regression analysis; (3) Results: Human milk was fed to 68% of the infants. According to multiple regression analysis, being fed any human milk at discharge and at  term-corrected and being fed exclusively human milk at term-corrected age were positively associated with fat-free mass content(β = −47.9, 95% confidence interval (CI) = −95.7; −0.18; p = 0.049; β = −89.6, 95% CI = −131.5; −47.7; p < 0.0001; β = −104.1, 95% CI = −151.4; −56.7, p < 0.0001); (4) Conclusion: Human milk feeding appears to be associated with fat-free mass deposition in late preterm infants. Healthcare professionals should direct efforts toward promoting and supporting breastfeeding in these vulnerable infants.

Body composition in late preterm infants according to percentile at birth

BACKGROUND

The data on body composition of late preterm infants, evaluated according to percentile at birth, are scarce. The study aimed to investigate body composition of late preterm infants, according to percentile at birth, and to compare their body composition with that of term newborns.

METHODS

A total of 122 (99 appropriate and 23 small for gestational age (SGA)) late preterm infants underwent growth and body composition assessment using an air displacement plethysmography system on the fifth day of life and at term. The reference group was composed of 42 healthy, term, breast-fed infants.

RESULTS

At birth, appropriate and SGA late preterm infants had lower fat mass and fat-free mass indexes than term newborns. The fat mass and fat-free mass content increased significantly throughout the study, irrespective of percentile at birth. At term, fat mass index, but not fat-free mass index, was higher in both appropriate and SGA late preterm infants than in term newborns.

CONCLUSION

Late preterm infants, irrespective of their percentile at birth, show postnatal growth characterized by predominant fat mass accretion. The potential long-term health clinical implications of these findings need to be further elucidated.

Intravenous lipids for preterm infants: a review

Extremely low birth weight infants (ELBW) are born at a time when the fetus is undergoing rapid intrauterine brain and body growth. Continuation of this growth in the first several weeks postnatally during the time these infants are on ventilator support and receiving critical care is often a challenge. These infants are usually highly stressed and at risk for catabolism. Parenteral nutrition is needed in these infants because most cannot meet the majority of their nutritional needs using the enteral route. Despite adoption of a more aggressive approach with amino acid infusions, there still appears to be a reluctance to use early intravenous lipids. This is based on several dogmas that suggest that lipid infusions may be associated with the development or exacerbation of lung disease, displace bilirubin from albumin, exacerbate sepsis, and cause CNS injury and thrombocytopena. Several recent reviews have focused on intravenous nutrition for premature neonate, but very little exists that provides a comprehensive review of intravenous lipid for very low birth and other critically ill neonates. Here, we would like to provide a brief basic overview, of lipid biochemistry and metabolism of lipids, especially as they pertain to the preterm infant, discuss the origin of some of the current clinical practices, and provide a review of the literature, that can be used as a basis for revising clinical care, and provide some clarity in this controversial area, where clinical care is often based more on tradition and dogma than science.

Body composition in late preterm infants in the first 10 days of life and at full term

AIM

To investigate changes in body weight, fat-free mass, fat mass and percentage of body fat during early life and at full-term postconceptional age (PCA) in preterm infants born after 32 gestational weeks and before 37.

METHODS

Twenty-nine late preterm infants underwent growth and body composition assessment by air displacement plethysmography (ADP) at the age of 4 days and at full-term PCA. In 25 of these infants, body composition was assessed three times between days four and nine of life. The preterm infants were compared with 29 full-term infants, matched for gestational age, sex and body weight.

RESULTS

There was a significant increase in birth weight and fat-free mass between days four and nine of life. Preterm infants had significantly more body fat 382 ± 180 g vs 287 ± 160 g than full-term infants at full-term PCA. Preterm infants showed poor linear growth between birth and full-term PCA.

CONCLUSION

Weight gain after the initial postnatal weight loss consists of gain in fat-free mass. At full-term PCA, preterm infants were stunted. When compared with full-term new born infants matched for body weight and gestational age, preterm infants had more body fat and a higher percentage of body fat.

Postnatal catch-up fat after late preterm birth

BACKGROUND

Late preterm birth accounts for 70% of preterm births. The aim of the study was to investigate the postnatal weight gain and weight gain composition changes in a cohort of late preterm infants.

METHODS

A total of 49 late preterm infants (mean birth weight 2,496 ± 330 g and gestational age 35.2 ± 0.7 wks) underwent growth and body composition assessment by an air displacement plethysmography system on the fifth day of life, at term, and at 1 and 3 mo of corrected age. The reference group was composed of 40 healthy, full-term, breast-fed infants.

RESULTS

The late preterm infants showed a Δ fat mass gain between birth and term-corrected age equal to 182%. As compared with full-term infants, at term and 1 mo of corrected age mean weight (3,396 ± 390 vs. 3,074 ± 409 g and 4,521 ± 398 vs. 4,235 ± 673 g, respectively) and percentage of fat mass (16.1 ± 4.6 vs. 8.9 ± 2.9 and 22.6 ± 4.2 vs. 17.4 ± 4.0, respectively) were significantly higher in late preterm infants, whereas no difference among groups was found at 3 mo.

CONCLUSION

Rapid postnatal catch-up fat was found in these infants. Further studies are needed to investigate whether this short-term increase in fat mass may modulate the risk of chronic diseases or represent an adaptive mechanism to extrauterine life.

Energy expenditure in very low birth weight newborns: a comparison between small and appropriate-for-gestational-age

AIMS

To compare resting energy expenditure (REE) in small- and appropriate-for-gestational-age very low birth weight newborns after reaching corrected at-term age.

METHODS

Observational study that included all clinically stable very low birth weight newborns admitted to a neonatal intensive care unit. The newborns were classified as small-for-gestational-age (SGA) and appropriate-for-gestational-age (AGA). Resting energy expenditure was measured using indirect calorimetry when the newborns reached at-term age.

RESULTS

A total of 51 newborns, of which 23 were SGA and 28 AGA, were included. There was no statistically significant difference in REE between the two groups, although the observed levels were higher than the reference values.

CONCLUSION

There is no statistical difference in resting expenditure energy between SGA and AGA infants when they reached term. The higher energy expenditure found in both groups may be explained by other factors related to prematurity and its complications and requires further investigation.

Energy expenditure in extremely low birth weight infants near time of hospital discharge

OBJECTIVE

To test the hypothesis that total energy expenditure is significantly higher in extremely low birth weight (ELBW) infants compared with healthy term infants near the time of discharge.

STUDY DESIGN

This study was designed to determine total energy expenditure and body composition in a group of ELBW infants nearing discharge receiving full-volume enteral feedings of fortified breast milk or postdischarge formula (Neosure) (n = 10; mean birth weight, 0.8 +/- 0.1 kg; mean gestational age, 26 +/- 0.8 weeks; mean age at study, 68 +/- 9 days; mean postconceptional age, 36 +/- 1 weeks) and compare them with healthy term newborns all receiving breast milk (n = 14; mean birth weight, 3.5 +/- 0.5 kg; mean gestational age, 39.0 +/- 1.4 weeks; mean age at study, 2.3 +/- 1 days). Body composition and total energy expenditure were measured using the doubly labeled water method over a 7-day period.

RESULTS

Mean total energy expenditure was significantly higher in the ELBW infants compared with the term infants (89 +/- 22 kcal/kg/day vs 58 +/- 19 kcal/kg/day; P <or= .001). Total energy expenditure normalized to fat-free mass was also significantly greater in the ELBW infants (98 +/- 3 kcal/kg/day vs 73 +/- 20 kcal/kg/day; P <or= .01).

CONCLUSIONS

The rate of total energy expenditure is greater in ELBW infants nearing discharge compared with normal healthy term infants. In the ELBW infants, higher energy intake compensates for their higher total energy expenditure.

Total body water in small- and appropriate- for gestational age newborns

OBJECTIVES

To ascertain total body water in small for gestational age (SGA) and appropriate for gestational age (AGA) newborns.

METHODS

SGA and AGA babies were matched by gestational age and studied from birth to term age. Criteria for exclusions were genetic syndromes, malformations, and congenital infections. Bioelectrical impedance was performed at two days of life (term infants), or at seven days of life and term age (preterm infants). Weight and length were measured by trained interviewers, and Z-score, weight/length ratio and Rohrer ponderal index was calculated.

RESULTS

Of the 54 infants evaluated, 28 were SGA (17 preterm) and 26 were AGA (15 preterm). Total body water was greater in SGA preterm babies at seven days of age (P=0.058) and at term age (P<0.0001). Weight/length ratio and Rohrer ponderal index increased towards term. Weight Z-score and anthropometric measures at term were significantly smaller in SGA babies. Being SGA and variation in Rohrer ponderal index influenced the variations in total body water.

CONCLUSIONS

SGA babies had greater total body water, and both groups presented insufficient increase in body solid mass, stressing the importance of nutritional support during neonatal care.

Energy intake, metabolic balance and growth in preterm infants fed formulas with different nonprotein energy supplements

OBJECTIVE

To study metabolic and energy balances, growth and composition of increased body mass in healthy preterm infants fed control formula or control formula with three different nonprotein energy supplements.

PATIENTS AND METHODS

Growing preterm infants (birth weight < 1,500 g and gestational age < 31 weeks) were fed standard preterm formula (control group) or the same formula enriched with three different nonprotein energy supplements. An energy supplement of 23 kcal/kg/day was achieved by adding medium-chain triglyceride and dextrinomaltose in three different caloric ratios: 33:66 in group A, 66:33 in group B, and 85:15 in group C. Energy balance was determined by open-circuit continuous (5-6 hours) measurements of energy expenditure, with simultaneous measurement of 24-hour urinary nitrogen excretion. Metabolic balance was determined by measurements of energy intake, energy oxidation, and energy output in urine and stool. The composition of body mass accretion was determined as the accretion of fat and protein in the total weight gain.

RESULTS

The fat accretion (4.9, 5.9, 6.2, and 3.8 g/kg/day in groups A, B, C and D, respectively) correlated directly with fat intake. Infants receiving standard energy intake had a fat percentage of weight gain significantly lower (28%) than that of the high-energy intake groups (31%, 40%, and 38% in groups A, B, and C, respectively). This difference corresponded to the results obtained from skinfold thickness measurements.

CONCLUSIONS

Excess nonprotein energy is stored as fat regardless of its source (fat or carbohydrate). High caloric and medium-chain triglyceride intake in otherwise healthy growing preterm infants does not promote nitrogen retention.

The role of parenteral lipids in supporting gluconeogenesis in very premature infants

We have previously demonstrated that very premature infants receiving glucose at 17 micromol/kg min plus appropriate supply of parenteral lipids (Intralipid) and amino acids (TrophAmine) maintained normoglycemia by glucose produced primarily via gluconeogenesis. The present study addressed the individual roles of parenteral lipids and amino acids in supporting gluconeogenesis. Fourteen premature infants (993 +/- 36 g 27 +/- 1 wk) (mean +/- SE) were studied for 8 h on d 5 +/- 1 of life. All infants were receiving standard TPN prior to the study. At start of study, the glucose infusion rate was decreased to approximately 17 micromol/kg min and either Intralipid (g + AA; n = 8) or TrophAmine (g + IL; n = 6) was discontinued. Data from 14 previously studied infants receiving glucose (approximately 17 micromol/kg min) + TrophAmine + Intralipid (g + AA + IL) are included for comparison. Gluconeogenesis was measured by [U-13 C]glucose, (g + AA) and (8 infants of the g + AA + IL group) or [2-13C]glycerol, (g + IL) and (6 infants of the g + AA + IL group). Infants studied by the same method were compared. Withdrawal of Intralipid resulted in decreased gluconeogenesis, 6.3 +/- 0.9 (g +AA) vs. 8.4 +/- 0.7 micromol/kg min (g + AA + IL) (p = 0.03). Withdrawal of TrophAmine affected neither total gluconeogenesis, 7.5 +/- 0.8 vs. 7.9 +/- 0.9 micromol/kg min nor gluconeogenesis from glycerol, 4.4 +/- 0.6 vs. 4.9 +/- 0.7 micromol/kg min (g+ IL and g + AA + IL groups, respectively). In conclusion, in parenterally fed very premature infants, lipids play a primary role in supporting gluconeogenesis.

Parenteral glycerol enhances gluconeogenesis in very premature infants

We have previously demonstrated that very premature infants receiving total parenteral nutrition maintain normoglycemia primarily by glucose produced via gluconeogenesis and that the lipid emulsion is most important in supporting gluconeogenesis. It is, however, not clear whether this is a result of the glycerol or the fatty acid constituent. The purpose of the present study was to determine the effect of intravenous supplemental glycerol alone on glucose production and gluconeogenesis. Twenty infants (birth weight, 1014 +/- 32 g; gestational age, 27 +/- 1 wk) were studied on d 4 +/- 1 (mean +/- SE). All infants received glucose at 17 micromol/kg x min for 9 h (after an initial study hour with 33 micromol/kg x min). Eight infants received no additional substrate during the study, and 12 infants received supplemental glycerol at 5 (n = 6) or 10 micromol/kg x min (n = 6) over the last 5 h of study. In infants receiving glucose alone, between period 1 (study hours 4-5) and period 2 (study hours 9-10), rates of glucose production ([U-13C]glucose) decreased from 12.9 +/- 1.2 to 7.4 +/- 0.9 micromol/kg x min (p < 0.01). This was the result of decreased glycogenolysis but no change in gluconeogenesis ([U-13C]glucose mass isotopomer distribution analysis) (5.1 +/- 0.6 versus 5.7 +/- 0.4 micromol/kg x min) (ns). Glycerol infusion at 5 and 10 micromol/kg x min, respectively, maintained glucose production (despite comparable decrease in glycogenolysis) by increasing gluconeogenesis from 4.3 +/- 0.2 to 6.3 +/- 0.5 (p < 0.03), and 6.0 +/- 0.7 to 8.8 +/- 0.8 micromol/kg/min (p < 0.01). In very premature infants, parenteral glycerol enhances gluconeogenesis and attenuates time dependent decrease in glucose production.

Adipose tissue in human infancy and childhood: an evolutionary perspective

Humans diverge from most mammals, including nonhuman primates, by depositing significant quantities of body fat in utero and are consequently one of the fattest species on record at birth. While explanations for the fat layer of human neonates have commonly assumed that it serves as insulation to compensate for hairlessness, empirical support for this hypothesis is presently weak. Whether the tissue's abundance at birth and growth changes in adiposity during infancy and childhood might be explained in light of its role as energy buffer has not been assessed, and this possibility is explored through development of a model of fat function and growth centered on two related hypotheses. The first is that the greater adiposity of human neonates is at least partially explainable as an accompaniment of the enlarged human brain, which demands a larger energy reserve to ensure that its obligatory needs are met when the flow of resources from mother or other caretakers is disrupted. The second is that age-related changes in the likelihood of experiencing such disruption have influenced the pattern of investment in the tissue, reflected today in peak adiposity during infancy and a decline to a leaner childhood period. Nutritional disruption is common at birth and until lactation is established, during which time human newborns survive from fats deposited prenatally, suggesting one possible explanation for the early onset of fat deposition. At weaning, the transition from breast milk to supplemental foods and the parallel transition from maternal to endogenous immune protection interact to increase the frequency and impact of nutritional disruption, and this may help explain why newborns devote roughly 70% of growth expenditure to fat deposition during the early postnatal months. Evidence is presented that fat stores are mobilized during infections, hinting at one possible mechanism underlying the association between nutritional status and infectious morbidity and mortality among infants in nutritionally stressed human populations. Consistent with the proposed hypothesis, well-fed infants acquire peak fat reserves by an age of peak prevalence of malnutrition, infectious disease, and fat reserve depletion in less-buffered contexts, and childhood--characterized by minimal investment in the tissue--is a stage of reduced risk of energy stress. The model presented here foregrounds energy storage in adipose tissue as an important life-history strategy and a means to modify mortality risk during the nutritionally turbulent period of infancy.

Influence of respiratory distress syndrome on body composition after preterm birth

AIM

To observe changes in body composition during the first week after birth, in preterm neonates with and without respiratory distress syndrome (RDS), so as to be able to provide optimal fluid and energy intake.

METHODS

Twenty four babies with RDS and 19 healthy preterm babies, with gestational ages ranging from 26-36 weeks, were studied daily for the first week after birth. Total body water (TBW) was measured using bioelectrical impedance analysis. The babies were weighed daily and a record made of fluid and energy intake. Body solids were calculated as the difference between body weight and TBW.

RESULTS

There was a highly significant reduction in body weight by the end of the week, with the RDS babies losing more than the healthy babies (RDS 7.6%; non-RDS 3.7%). There was no significant difference in the amount of TBW at birth in the babies with and without RDS (RDS 85.1%; non-RDS 85.5%) and both groups lost the same amount of body water (RDS 10.9%; non-RDS 9.9%) by the end of the first week. The amount of total body water lost was unrelated to the volume of fluid administered. There was a loss of body solids during the first day in the RDS group, but, overall, there was a highly significant increase in both groups between birth and day 7, which was greater in the healthy babies (RDS 13.0%; non-RDS 42.7%).

CONCLUSIONS

Loss of body water after birth occurs to the same extent in healthy preterm neonates and in babies with RDS and is unrelated to the volume of fluid administered. Given adequate nutritional support, an increase in body solids can accompany early postnatal weight loss and begins almost immediately after birth, in both healthy preterm babies and babies with RDS.

Postnatal weight velocity patterns in very low birthweight infants

The care of very-low-birth-weight infants has improved over the years with continuing changes in medical and nutritional management. In view of these changes, there is a need to study the pattern of postnatal weight gain. Postnatal weight gain patterns of 32 very-low-birth-weight infants were examined during the first two months of life. Their mean gestational age was 29.5 +/- 2.3 weeks and mean birth weight was 1255 +/- 258 grams. The babies were weighed daily and weight changes were expressed in gram/day. All data were accurately recorded. When mean weight gain profiles were obtained by computing increments at 1, 3, 7 and 14 day intervals, the babies weight gain showed a non-linear pulsatile pattern which did not change even after full enteral nutrition had been established. This study demonstrates that weight velocity profile in very-low-birth-weight infants is not linear as expected from available standard curves and these data might therefore be considered while monitoring the adequacy of the increments of the weight gain of the individual subjects.