Calciuria and aminoaciduria in very low birth weight infants fed a high-mineral premature formula with varying levels of protein

High protein intake on later outcomes in preterm children: a systematic review and meta-analysis

BACKGROUND

Appropriate protein intake is crucial for growth and development in children born preterm. We assessed the effects of high (HP) versus low protein (LP) intake on neurodevelopment, growth, and biochemical anomalies in these children.

METHODS

Randomised and quasi-randomised trials providing protein to children born preterm (<37 completed weeks of gestation) were searched following PRISMA guideline in three databases and four registers (PROSPERO registration CRD42022325659). Random-effects model was used for assessing the effects of HP (≥3.5 g/kg/d) vs. LP (<3.5 g/kg/d).

RESULTS

Data from forty-four studies (n = 5338) showed HP might slightly reduce the chance of survival without neurodisability at ≥12 months (four studies, 1109 children, relative risk [RR] 0.95 [95% CI 0.90, 1.01]; P = 0.13; low certainty evidence) and might increase risk of cognitive impairment at toddler age (two studies; 436 children; RR 1.36 [0.89, 2.09]; P = 0.16; low certainty evidence). At discharge or 36 weeks, HP intake might result in higher weight and greater head circumference z-scores. HP intake probably increased the risk of hypophosphatemia, hypercalcemia, refeeding syndrome and high blood urea, but reduced risk of hyperglycaemia.

CONCLUSIONS

HP intake for children born preterm may be harmful for neonatal metabolism and later neurodisability and has few short-term benefits for growth.

IMPACT STATEMENT

Planned high protein intake after birth for infants born preterm might be harmful for survival, neurodisability and metabolism during infancy and did not improve growth after the neonatal period. Protein intake ≥3.5 g/kg/d should not be recommended for children born preterm.

Effects of higher protein formula with improved fat blend on growth, feeding tolerance and nutritional biomarkers in preterm infants: A double-blind, randomized, controlled clinical trial

BACKGROUND

Preterm formulas containing greater protein:energy ratio are beneficial for non-breastfed infants, since protein is critical for promoting catch-up growth and synthesis of lean body mass. Additionally, formulas containing enriched sn-2 palmitate (sn-2) and reduced medium chain triglycerides (MCTs) may support better feeding tolerance and nutrient utilization.

METHODS

The objective of this randomized, controlled, double-blinded clinical trial is to evaluate growth, feeding tolerance and nutritional biomarkers of preterm infants with birth weight ≤2000g and gestational age ≤33wks from one neonatal unit in Vietnam receiving experimental formula (EF, n = 80) containing higher protein level of 3.4 g/100 kcal and improved fat blend with enriched sn-2 and modified level of MCTs or isocaloric control formula (CF, n = 80) containing protein level of 2.9 g/100 kcal and standard fat blend. The differences in weight gain (g/d; primary endpoint) from day 1 (D1) of full enteral feeding (FEF) until D21 between groups was evaluated for non-inferiority (margin = -2.5  g/d) and superiority (margin = 0  g/d).

RESULTS

Mean weight gain was 3.09  g/d greater in EF than CF; the lower limit of 95% CI (0.31  g/d) exceeded both non-inferiority and superiority margins. There was no significant difference in length-for-age and head circumference-for-age z-score. By D79, the mean change in weight-for-age z-scores from D1 in EF group (+0.76 SDs) surpassed the criteria for catch-up growth (+0.67 SDs). Infants in the EF group (vs. CF) tended to have softer stools (EF = 3.2 ± 0.59 vs. CF = 3.4 ± 0.58; P = 0.07) based on 5-point scale (1 = watery, 5 = hard). Difference in blood urea nitrogen and biomarkers for bone mineral status (i.e., plasma phosphorus, alkaline phosphatase and urinary calcium/phosphorus ratio) between EF and CF on FEF Day 21 reached statistical significance (P < 0.05) but all mean values stayed within normal clinical ranges for both groups.

CONCLUSION

Preterm formula with greater protein:energy ratio and new fat blend is safe, nutritionally suitable, well-tolerated, and improves catch-up weight gain of preterm infants. Clinical trial registry identifier is NCT03055052 (ClinicalTrials.gov).

Higher versus lower protein intake in formula-fed low birth weight infants

BACKGROUND

The ideal quantity of dietary protein for formula-fed low birth weight infants is still a matter of debate. Protein intake must be sufficient to achieve normal growth without leading to negative effects such as acidosis, uremia, and elevated levels of circulating amino acids.

OBJECTIVES

To determine whether higher (≥ 3.0 g/kg/d) versus lower (< 3.0 g/kg/d) protein intake during the initial hospital stay of formula-fed preterm infants or low birth weight infants (< 2.5 kilograms) results in improved growth and neurodevelopmental outcomes without evidence of short- or long-term morbidity. Specific objectives were to examine the following comparisons of interventions and to conduct subgroup analyses if possible. 1. Low protein intake if the amount was less than 3.0 g/kg/d. 2. High protein intake if the amount was equal to or greater than 3.0 g/kg/d but less than 4.0 g/kg/d. 3. Very high protein intake if the amount was equal to or greater than 4.0 g/kg/d.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2019, Issue 8), in the Cochrane Library (August 2, 2019); OVID MEDLINE Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE(R) Daily, and Ovid MEDLINE(R) (to August 2, 2019); MEDLINE via PubMed (to August 2, 2019) for the previous year; and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (to August 2, 2019). We also searched clinical trials databases and the reference lists of retrieved articles for randomized controlled trials (RCTs) and quasi-randomized trials.

SELECTION CRITERIA

We included RCTs contrasting levels of formula protein intake as low (< 3.0 g/kg/d), high (≥ 3.0 g/kg/d but < 4.0 g/kg/d), or very high (≥ 4.0 g/kg/d) in formula-fed hospitalized neonates weighing less than 2.5 kilograms. We excluded studies if infants received partial parenteral nutrition during the study period, or if infants were fed formula as a supplement to human milk.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane and the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

We identified six eligible trials that enrolled 218 infants through searches updated to August 2, 2019. Five studies compared low (< 3 g/kg/d) versus high (3.0 to 4.0 g/kg/d) protein intake using formulas that kept other nutrients constant. The trials were small (n = 139), and almost all had methodological limitations; the most frequent uncertainty was about attrition. Low-certainty evidence suggests improved weight gain (mean difference [MD] 2.36 g/kg/d, 95% confidence interval [CI] 1.31 to 3.40) and higher nitrogen accretion in infants receiving formula with higher protein content (3.0 to 4.0 g/kg/d) versus lower protein content (< 3 g/kg/d), while other nutrients were kept constant. No significant differences were seen in rates of necrotizing enterocolitis, sepsis, or diarrhea. We are uncertain whether high versus low protein intake affects head growth (MD 0.37 cm/week, 95% CI 0.16 to 0.58; n = 18) and length gain (MD 0.16 cm/week, 95% CI -0.02 to 0.34; n = 48), but sample sizes were small for these comparisons. One study compared high (3.0 to 4.0 g/kg/d) versus very high (≥ 4 g/kg/d) protein intake (average intakes were 3.6 and 4.1 g/kg/d) during and after an initial hospital stay (n = 77). Moderate-certainty evidence shows no significant differences in weight gain or length gain to discharge, term, and 12 weeks corrected age from very high protein intake (4.1 versus 3.6 g/kg/d). Three of the 24 infants receiving very high protein intake developed uremia.

AUTHORS' CONCLUSIONS

Higher protein intake (≥ 3.0 g/kg/d but < 4.0 g/kg/d) from formula accelerates weight gain. However, limited information is available regarding the impact of higher formula protein intake on long-term outcomes such as neurodevelopment. Research is needed to investigate the safety and effectiveness of protein intake ≥ 4.0 g/kg/d.

Influence of Feeding Types during the First Months of Life on Calciuria Levels in Healthy Infants: A Secondary Analysis from a Randomized Clinical Trial

Background/Aims: Dietary factors can modify calciuria. We aim to investigate urinary calcium excretion in healthy infants according to their protein. Methods: Secondary data analysis from a randomized clinical trial where healthy term infants were randomized after birth to a higher (HP) or lower (LP) protein content formula that was consumed until age 1 year. A non-randomized group of breastfed (BF) infants was used for reference. Anthropometry, dietary intakes and calciuria (calcium/creatinine ratios) from spot urine samples were assessed at ages 3 and 6 months. At 6 months, the kidney volumes were assessed using ultrasonography, and the serum urea and creatinine levels were determined. Results: BF infants showed the highest calciuria levels, followed by the HP and the LP groups (p < 0.001 for all comparisons). Either protein intakes or formula types modulated the calciuria in linear regression models adjusted for other influencing dietary factors. The usual cut-off values classified 37.8% (BF), 16.8% (HP) and 4.9% (LP) of the infants as hypercalciuric. Conclusions: Feeding types during the first months of life affect calciuria, with BF infants presenting the highest levels. We propose new cut-off values, based on feeding types, to prevent the overestimation in hypercalciuria diagnoses among BF infants.

Does Amount of Protein in Formula Matter for Low-Birthweight Infants? A Cochrane Systematic Review

BACKGROUND

High protein intake may be associated with negative consequences such as acidosis, uremia, and elevated levels of circulating amino acids (eg, phenylalanine levels). We performed a systematic review of randomized controlled trials to determine whether formula-fed low-birthweight infants could tolerate protein intakes>or=3.0 g/kg/d in their initial hospital stay, without adverse consequences.

METHODS

Randomized controlled trials contrasting levels of protein intakes as low (<3.0 g/kg/d), high (>or=3.0 g/kg/d but <4.0 g/kg/d), or very high protein intake (>or=4.0 g/kg/d) while other nutrients were held constant, were identified through a systematic search of the literature. Standard methods of the Cochrane Collaboration were used by 2 independent reviewers, with the third reviewer facilitating consensus decision making.

RESULTS

A meta-analysis of 5 randomized trials indicated improved weight gain (weighted mean difference [WMD] 2.36 g/kg/d; 95% confidence interval [CI] 1.31-3.40) and higher nitrogen accretion (WMD 143.7 mg/kg/d; 95% CI 128.7-158.8) with high (>or=3.0 g/kg/d but <4.0 g/kg/d) compared with low (<3.0 g/kg/d) protein intakes while other nutrients were kept constant. No data were available for IQ or Bayley scores at 18 months or later or for very high protein intakes (>or=4.0 g/kg/d). No significant differences were seen in rates of necrotizing enterocolitis, sepsis, or diarrhea.

CONCLUSIONS

Accelerated weight and nitrogen accretion were noted with higher protein intakes in "healthy" formula-fed low-birthweight infants. This benefit could not be weighed against the adverse consequences of elevated blood urea nitrogen levels and increased metabolic acidosis and neurodevelopmental abnormalities.

Protein Intake and Growth in Preterm Infants: A Systematic Review

Objective. This review aimed to investigate the relationship between varying levels of enteral protein intake and growth in preterm infants, regardless of feeding method. Data Sources. Electronic databases were searched for relevant studies, as were review articles, reference lists, and text books. Study Selection. Trials were included if they were randomized or quasirandomized, participants were <37 weeks gestation at birth, and protein intakes were intentionally or statistically different between study groups. Trials reporting weight, length, and head circumference gains in infants fed formula, human milk, or fortified human milk were included. Data Extraction. Studies were categorized by feeding-type and relevant data were extracted into summary tables by one reviewer and cross-checked by a second. Data Synthesis. A meta-analysis could not be conducted due to extensive variability among studies; thus, results were synthesized graphically and narratively. Twenty-four trials met the inclusion criteria and were included in a narrative synthesis and 19 in a graphical synthesis of study results. Conclusions. There was extensive variability in study design, participant characteristics, and study quality. Nonetheless, results are fairly consistent that higher protein intake results in increased growth with graphical representation indicating a potentially linear relationship. Additionally, intakes as high as 4.5 g/kg/day were shown to be safe in infants weighing >1000 g.

Higher versus lower protein intake in formula-fed low birth weight infants

BACKGROUND

The ideal quantity of dietary protein for formula-fed low birth weight infants is still a matter of debate. Protein intake must be sufficient to achieve normal growth without negative effects such as acidosis, uremia, and elevated levels of circulating amino acids.

OBJECTIVES

To determine whether higher (≥ 3.0 g/kg/d) versus lower (< 3.0 g/kg/d) protein intake during the initial hospital stay of formula-fed preterm infants or low birth weight infants (< 2.5 kilograms) results in improved growth and neurodevelopmental outcomes without evidence of short- and long-term morbidity.To examine the following distinctions in protein intake. 1. Low protein intake if the amount was less than 3.0 g/kg/d. 2. High protein intake if the amount was equal to or greater than 3.0 g/kg/d but less than 4.0 g/kg/d. 3. Very high protein intake if the amount was equal to or greater than 4.0 g/kg/d.If the reviewed studies combined alterations of protein and energy, subgroup analyses were to be carried out for the planned categories of protein intake according to the following predefined energy intake categories. 1. Low energy intake: less than 105 kcal/kg/d. 2. Medium energy intake: greater than or equal to 105 kcal/kg/d and less than or equal to 135 kcal/kg/d. 3. High energy intake: greater than 135 kcal/kg/d.As the Ziegler-Fomon reference fetus estimates different protein requirements for infants based on birth weight, subgroup analyses were to be undertaken for the following birth weight categories. 1. < 800 grams. 2. 800 to 1199 grams. 3. 1200 to 1799 grams. 4. 1800 to 2499 grams.

SEARCH METHODS

The standard search methods of the Cochrane Neonatal Review Group were used. MEDLINE, CINAHL, PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL; The Cochrane Library) were searched.

SELECTION CRITERIA

Randomized controlled trials contrasting levels of formula protein intake as low (< 3.0 g/kg/d), high (≥ 3.0 g/kg/d but < 4.0 g/kg/d), or very high (≥ 4.0 g/kg/d) in formula-fed hospitalized neonates weighing less than 2.5 kilograms were included. Studies were excluded if infants received partial parenteral nutrition during the study period or were fed formula as a supplement to human milk. Studies in which nutrients other than protein also varied were added in a post-facto analysis.

DATA COLLECTION AND ANALYSIS

The standard methods of the Cochrane Neonatal Review Group were used.

MAIN RESULTS

Five studies compared low versus high protein intake. Improved weight gain and higher nitrogen accretion were demonstrated in infants receiving formula with higher protein content while other nutrients were kept constant. No significant differences were seen in rates of necrotizing enterocolitis, sepsis, or diarrhea.One study compared high versus very high protein intake during and after an initial hospital stay. Very high protein intake promoted improved gain in length at term, but differences did not remain significant at 12 weeks corrected age. Three of the 24 infants receiving very high protein intake developed uremia.A post-facto analysis revealed further improvement in all growth parameters in infants receiving formula with higher protein content. No significant difference in the concentration of plasma phenylalanine was noted between high and low protein intake groups. However, one study (Goldman 1969) documented a significantly increased incidence of low intelligence quotient (IQ) scores among infants of birth weight less than 1300 grams who received a very high protein intake (6 to 7.2 g/kg).

AUTHORS' CONCLUSIONS

Higher protein intake (≥ 3.0 g/kg/d but < 4.0 g/kg/d) from formula accelerates weight gain. However, limited information is available regarding the impact of higher formula protein intake on long-term outcomes such as neurodevelopmental abnormalities. Available evidence is not adequate to permit specific recommendations regarding the provision of very high protein intake (> 4.0 g/kg/d) from formula during the initial hospital stay or after discharge.

Metabolic bone disease and bone mineral density in very preterm infants

OBJECTIVES

To evaluate bone mineral density (BMD) in preterm neonates at discharge and identify the optimum cutoff values for serum alkaline phosphatase (ALP) and phosphorus (P) concentrations to diagnose the severity of metabolic bone disease of prematurity.

STUDY DESIGN

A total of 336 preterm neonates (≤ 31 weeks' gestation and birth weight ≤ 1500 g) were prospectively evaluated for BMD before discharge using dual-energy X-ray absorptiometry.

RESULTS

BMD reference values (at ALP ≤ 500 IU/L) were measured in 279 patients. BMD was classified as poor (<10th percentile) at <0.068 g/cm(2), fair (10th-25th percentile) at 0.068-0.081 g/cm(2), good (25th-75th percentile) at 0.081-0.112 g/cm(2), and very good (>75th percentile) at >0.112 g/cm(2). Increased BMD was associated with a higher birth weight, short duration of parenteral nutrition, and the absence of small for gestational age status, patent ductus arteriosus, intraventricular hemorrhage, and other clinical variables. Metabolic bone disease of prematurity was absent (ALP ≤ 500 IU/L) in 279 cases (83.0%), mild (ALP >500 IU/L and P ≥ 4.5 mg/dL) in 46 cases (13.7%), and severe (ALP >500 IU/L and P <4.5 mg/dL) in 11 cases (3.3%).

CONCLUSIONS

A BMD >0.068 g/cm(2) at discharge indicated a 90.3% probability of not developing metabolic bone disease of prematurity. The factors independently associated with increased BMD included higher birth weight, short duration of parenteral nutrition, absence of intraventricular hemorrhage, exclusive feeding of fortified breast milk, and older age at discharge.

Enteral intake for very low birth weight infants: what should the composition be?

Providing optimal nutrition to satisfy the growth needs of very low birth weight infants is critical. The available preterm formulas and fortified human milk diets provide protein intakes of approximately 3.5 to 3.6 g/kg/d when volumes sufficient to provide 120 kcal/kg/d are fed to these infants. These intakes support growth and protein accretion at about or slightly greater than intrauterine rate and lead to relatively increased fat deposition. However, most very low birth infants fed these diets remain below the 10th percentile of the intrauterine growth standards at discharge. There is clear evidence that, with respect to growth, very low birth infants are likely to benefit from a higher protein intake; however, there is no clear evidence that energy intakes greater than 120 kcal/kg/d are needed. Although the upper limit of protein intake and the ideal protein:energy ratio remain controversial, there is enough evidence to support the beneficial and safe use of formulas providing protein:energy ratio of 3.2 to 3.3 g/100 kcal.

Higher versus lower protein intake in formula-fed low birth weight infants

BACKGROUND

The ideal quantity of dietary protein for formula-fed low birth weight infants < 2.5 kilograms is still a matter of controversy and debate. In premature infants, the protein intake must be sufficient to achieve normal growth without negative effects such as acidosis, uremia, and elevated levels of circulating amino acids (e.g. phenylalanine levels). This systematic review evaluates the benefits and risks of higher (>= 3.0 g/kg/day) versus lower (< 3.0 g/kg/day) protein intakes during the initial hospital stay of formula-fed preterm infants < 2.5 kilograms.

OBJECTIVES

To determine whether higher (>= 3.0 g/kg/day) versus lower (< 3.0 g/kg/day) protein intakes during the initial hospital stay of formula-fed preterm infants < 2.5 kilograms result in improved growth and neurodevelopmental outcomes without evidence of short and long-term morbidity.

SEARCH STRATEGY

Two review authors searched MEDLINE (1966 - May 2005), CINAHL (1982 - May 2005), PubMed (1966 - May 2005), EMBASE (1980 - May 2005), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2005), abstracts, conferences and symposia proceedings from Society of Pediatric Research, and American Academy of Pediatrics. Cross references were reviewed independently for additional relevant titles and abstracts for articles up to fifty years old.

SELECTION CRITERIA

Randomized controlled trials contrasting levels of formula protein intakes as low (< 3.0 g/kg/day), high (=> 3.0 g/kg/day but < 4.0 g/kg/day), or very high protein intake (=> 4.0 g/kg/day) during hospitalization of neonates less than 2.5 kilograms at birth who were formula-fed. Studies were not included if infants received partial parenteral nutrition during the study period or were fed formula as a supplement to human milk. Given the small number of studies that met all inclusion criteria, studies in which nutrients other than protein also varied (> 10% relative difference) were added in a post-facto analysis.

DATA COLLECTION AND ANALYSIS

Two review authors used standard methods of the Cochrane Collaboration and of the Cochrane Neonatal Review Group to independently assess trial eligibility and quality, and extracted data. In a 3-arm trial where two groups fell within the same predesignated protein intake group, weighted means and pooled standard deviations were calculated.

MAIN RESULTS

The literature search identified 37 studies, of which five met all the inclusion criteria. All five studies compared low (< 3.0 g/kg/day) to high protein intakes (=> 3.0 g/kg/day but < 4.0 g/kg/day). The overall analysis revealed an improved weight gain (WMD 2.36 g/kg/day, 95% CI 1.31, 3.40) and higher nitrogen accretion (WMD 143.7 mg/kg/day, 95% CI 128.7, 158.8) in infants receiving formula with higher protein content while other nutrients were kept constant. None of the studies reported IQ or Bayley scores at 18 months or later. No significant differences were seen in rates of necrotizing enterocolitis, sepsis or diarrhea. Of three studies included in the post-facto analysis, only one could be included in the meta-analysis. The post-facto analysis revealed further improvement in all growth parameters in infants receiving formula with higher protein content (weight gain: WMD 2.53 g/kg/day, 95% CI 1.62, 3.45, linear growth: WMD 0.16 cm/week, 95% CI 0.03, 0.30, and head growth: WMD 0.23, 95% CI 0.12, 0.35). There was no significant difference (WMD 0.25, 95% CI -0.20, 0.70) in the concentration of plasma phenylalanine between the high and low protein intake groups. One study (Goldman 1969) in the post-facto analysis documented a significantly increased incidence of low IQ scores, below 90, in infants of birth weight less than 1300 grams who received a very high protein intake (6 to 7.2 g/kg/day).

AUTHORS' CONCLUSIONS

This systematic review suggests that higher protein intake (=> 3.0 g/kg/day but < 4.0 g/kg/day) from formula accelerates weight gain. Based on increased nitrogen accretion rates, this most likely indicates an increase in lean body mass. Although accelerated weight gain is considered to be a positive effect, increase in other outcome measures examined may represent a negative or ambivalent effect. These include elevated blood urea nitrogen levels and increased metabolic acidosis. Limited information was available regarding the impact of higher formula protein intakes on long term outcomes such as neurodevelopmental abnormalities. As determined in this review, existing research literature on this topic is not adequate to make specific recommendations regarding the provision of very high protein intake (> 4.0 g/kg/day) from formula.

Protein requirements in preterm infants: effect of different levels of protein intake on growth and body composition

This study compares growth and body composition in preterm infants (< or =1750 g birth weight, < or =34 wk gestation) fed three iso-caloric formulas (80 kcal/100 mL) with different protein concentrations (A = 3.3 g/100 kcal, B = 3.0 g/100 kcal, C = 2.7 g/100 kcal). The study began when full enteral feeding (150 mL/kg/d) was established and lasted until term plus 12 wk corrected age (T + 12 wca). Nutrient intake was closely monitored throughout the study; daily during initial hospital stay and following discharge averaged between each clinic visit. Anthropometry and serum biochemistries were determined weekly during initial stay and at each clinic visit. Body composition was measured after hospital discharge and at T + 12 wca. Seventy-seven infants were recruited. No differences were detected in birth/enrollment characteristics between the groups. Protein intake was closely paralleled by changes in serum urea nitrogen and differed between the groups. Infants in group A were heavier and longer and had greater head circumference at discharge, but this was confounded by a slightly older corrected age in this group. There were no significant anthropometric differences at term or T + 12 wca. No differences were detected in body composition between the groups following discharge or at T + 12 wca. An intake of 3.3 g/100 kcal appears safe and may promote increased growth before initial hospital discharge. After discharge, intakes greater than 2.7 g/100 kcal do not appear to offer clear advantage. Further studies are needed to more precisely define protein requirements in these nutritionally at-risk infants.

Urinary excretion of calcium and phosphate in preterm infants

The aims of this study were to determine reference ranges for the urinary calcium (UCa/Cr) and phosphate (UPO(4)/Cr) creatinine ratios and to study factors influencing these ratios in a representative population of preterm infants managed according to current nutritional guidelines. Spot urine samples were obtained from 186 preterm infants (gestation 24-34 weeks) for measurement of UCa/Cr and UPO(4)/Cr ratios as part of a routine metabolic bone screening program, once every 2-4 weeks from the 3rd to the 18th week of life. Data were also collected on gender, appropriate or small for gestational age (SGA), nutrition [total parenteral nutrition (TPN), preterm or term formula, and breast milk], plasma Ca, P0(4), urea, and electrolytes and on the use of drugs (frusemide, dexamethasone, and theophylline). Data from infants treated with any of these three drugs were analyzed separately and not included in establishing the reference ranges for UCa/Cr and UPO(4)/Cr. The mean gestational age of the study population was 28 weeks (range 24-34 weeks). The 95th percentile for UCa/Cr at 3 weeks of age was 3.8 mmol/mmol and decreased significantly with increasing postnatal age (P<0.001). The 95th per-centile for UPO(4)/Cr was 26.69 mmol/mmol at 3 weeks of age, but this did not change significantly with increasing postnatal age (P=0.296). On univariate analysis there was no significant association of UCa/Cr and UPO(4)/Cr with gender and type of enteral nutrition. The UCa/Cr was lower in infants who were SGA (P=0.013) and with low plasma Ca (P=0.008). Infants on TPN had significantly higher UCa/Cr (P =0.019) and lower UPO(4)/Cr ratios(P<0.001). Multivariate analysis confirmed the decrease in UCa/Cr ratio with increasing postnatal age, but the SGA effect was eliminated. The use of furosemide(P<0.001) and theophylline (P=0.003) was associated with a significant increase in the UCa/Cr ratio. The use of dexamethasone was also associated with an increase in UCa/Cr ratio, but this did not achieve statistical significance (P=0.339). The use of furosemide, theophylline,and dexamethasone had no effect on UPO(4)/Cr. We report a reference range for UCa/Cr and UPO(4)/Cr ratios and factors influencing these ratios in a representative population of preterm infants between 24 and 34 weeks gestation, managed according to current nutritional guide-lines.

Areal bone mineral density of the lumbar spine in 80 premature newborns: a prospective and longitudinal study

BACKGROUND

Maximum bone mass accretion in the fetal skeleton is acquired during the third trimester of gestation, and may be compromised in premature newborns.

OBJECTIVE

To ascertain the incidence and evolution of osteopenia, a longitudinal study was performed to evaluate areal bone mineral density (aBMD) in the lumbar spine in premature newborns followed during the first 2 years of life.

METHODS

aBMD values were assessed in lumbar spine (L2-L4) by DEXA and expressed as grams hydroxyapatite/cm2 in 80 premature newborns, 41 boys and 39 girls, of gestational ages 24.5-35.7 weeks. aBMD values were evaluated at (mean+/-SD) 0.2+/-0.1 years (at discharge from the neonatal unit), 0.9+/-0.2 years and 2.0+/-0.5 years of postnatal age, and compared with those of age- and sex-matched full-term newborns with normal intrauterine and postnatal growth.

RESULTS

aBMD values recovered progressively from the first to the third evaluations, and were 0.139+/-0.06 g/cm2 (-2.4+/-1.4 SDS) at 0.2+/-0.1, 0.270+/-0.06 g/cm2 (-1.0+/-1.0 SDS) at 0.9+/-0.2 and 0.410 g/cm2 (-0.08+/-1.0 SDS) at 2.0+/-0.5 years.

CONCLUSIONS

Our data show a significant catch-up of aBMD, reaching values similar to those of full-term newborns at the age of 0.2+/-0.5 years, regardless of the gestational age at birth.

Nutrient accretion in preterm infants fed formula with different protein:energy ratios

BACKGROUND

Although standard formulas for preterm infants promote intrauterine rates of weight gain, fat deposition in preterm infants fed these formulas has been reported to be considerably higher than that in the fetus. We hypothesized that a preterm infant formula with a higher protein:energy (P:E) ratio would promote accretion rates of fat, fat-free mass, and minerals closer to those of the fetus.

METHODS

As part of a larger study to determine whether accretion rates of fat and fat-free mass closer to those of the fetus can be achieved with a higher P:E ratio, we present a descriptive analysis of 72-h nutrient balance studies performed on a subset (n = 15/30) of the infants randomly assigned to be fed formula with a P:E ratio of either 3.2 g/100 kcal or 2.6 g/100 kcal.

RESULTS

Despite the higher intake and net absorption of nitrogen by infants fed the higher P:E formula, there was no statistically significant difference in net nitrogen retention between groups. There also were no statistically significant differences between groups in digestible energy, metabolizable energy, energy expenditure, or energy storage. Thus, partitioning of stored energy as protein and fat did not differ between groups. The retention of calcium, phosphorus, sodium, potassium, copper, and zinc also did not differ between groups, and nitrogen intake did not affect mineral retention.

CONCLUSIONS

In this study, formula for preterm infants with a P:E ratio of 3.2 g/100 kcal vs. 2.6 g/100 kcal provided no apparent benefit in terms of the proportion of fat to lean tissue accretion as determined from nutrient balance data.

Metabolic bone disease of prematurity

Metabolic bone disease is recognized with increasing frequency in very-low-birth-weight infants. Radiological changes characteristic of rickets have been found in 55% of infants with a birth weight of less than 1000 g and in 23% of infants weighing less than 1500 g at birth. Twenty-four per cent of infants with a birth weight of less than 1500 g have fractures. The main aetiological factor is insufficient phosphorus supplementation. The aetiology is, however, multifactorial and also includes calcium deficiency, vitamin D deficiency, certain drugs, aluminium loading and immobilisation. The method of choice in detecting subclinical mineral bone disease of prematurity is measurement of bone mineral density, but there is as yet no single good diagnostic method available for premature infants. The optimal mineral and vitamin D requirement of the premature infant must be established so that proper recommendations can be given. The current recommended vitamin D dose in Europe (ESPGAN 800-1000 IU/day) is probably too high when extra minerals are supplied. Moreover, the duration of mineral supplementation may need to be continued until the infant has reached a body weight of 3.5 kg. This article deals with the aetiology, pathogenesis, diagnosis and future prospects of metabolic bone disease of prematurity.