Multicentre trial on feeding low birthweight infants: effects of diet on early growth

Early sodium intake and later blood pressure in preterm infants

The relation between early salt intake and later hypertension is debated. As part of a larger feeding study, 347 preterm infants were randomly assigned to receive early diets differing grossly in sodium content. Feeding a high sodium preterm formula in the neonatal period did not influence arterial blood pressure at 18 months (corrected) age.

Improved bone mineralization and growth in premature infants fed fortified own mother's milk

"Preterm" human milk fortified with protein (0.85 gm/dL), calcium (90 mg/dL), and phosphorus (45 mg/dL) was compared with unfortified preterm human milk as a feeding for low birth weight infants. Additionally, a special formula for low birth weight infants (Similac Special Care (SC), 20 cal/oz), was compared with a standard 20 cal/oz formula (Similac). Bone mineral content (BMC), as measured by photon absorptiometry, improved in the study groups fed fortified human milk and Similac SC formula during the first 6 weeks of full oral feedings. Even though the intakes of calcium in the groups fed fortified human milk and Similac SC formula approached the intrauterine requirement for Ca during the third trimester of pregnancy (150 mg/kg/d), the values for BMC in these two groups (37 to 39 mg/cm) at the completion of the study were still considerably less than the intrauterine values for radial BMC at 36 to 37 weeks gestational age (72.6 +/- 14.1 mg/cm). Furthermore, the relative phosphorus deficiency (as determined by increased urinary Ca excretion and increased renal tubular reabsorption of phosphate) in the human milk groups occurred with or without supplements of Ca and P. Rate of weight gain in the fortified human milk group was greater than that of the unfortified human milk group and was comparable to that of infants fed Similac SC formula. Rate of weight gain for the unfortified human milk group was similar to that of infants fed Similac formula containing 20 cal/oz. However, none of the four feeding groups exceeded the 50th percentile for weight at the time of discharge (36 to 37 weeks postconceptional age). The results suggest that fortifying preterm human milk with Ca, P, and protein for low birth weight infants will improve bone mineralization and rate of growth to levels comparable to those achieved with a special formula containing high amounts of protein, Ca, and P.

Maternal fatness and viability of preterm infants

To investigate the effect of maternal fatness on the mortality of infants born preterm up to the corrected age of 18 months 795 mother-infant pairs were studied. Maternal fatness was defined by Quetelet's index (weight/(height] and all infants weighed less than 1850 g at birth. In 771 mother-infant pairs maternal age, complications of pregnancy, mode of delivery, parity, social class, and the baby's sex and gestation were analysed by a logistic regression model for associations with infant mortality (but deaths from severe congenital abnormalities and those occurring during the first 48 hours after birth were excluded). In a subgroup of 284 mother-infant pairs all infant deaths except those from severe congenital abnormalities were analysed in association with the infant's birth weight and gestation and the mother's height and weight; this second analysis included another 24 infants who had died within 48 hours after birth. In the first analysis mortality overall was 7% (55/771), rising from 4% (71/173) in thin mothers (Quetelet's index less than 20) to 15% (6/40) in mothers with grades II and III obesity (Quetelet's index greater than 30). After adjusting for major demographic and antenatal factors, including serious complications of pregnancy, maternal fatness was second in importance only to length of gestation in predicting death of infants born preterm. In the second analysis mortality overall was 15% (44/284), rising from 9% (5/53) in thin mothers to 47% (8/17) in mothers with grades II and III obesity. In both analyses the relative risk of death by 18 months post-term was nearly four times greater in infants born to obese mothers than in those born to thin mothers. In addition, maternal fatness was associated with reduced birth weight, whereas it is associated with macrosomia in term infants. These data differ fundamentally from those reported in full term babies of obese mothers. It is speculated that the altered metabolic milieu in obesity may reduce the ability of the fetus to adapt to extrauterine life if it is born preterm.

Factors associated with maternal choice to provide breast milk for low birthweight infants

Factors associated with maternal choice to provide milk for premature infants were investigated in 925 mother/infant pairs in five hospitals. A well educated, married, primiparous mother aged 20 or over who delivered a baby boy by caesarean section was nearly 1000 times more likely to choose to express her milk than a mother who was poorly educated, single, multiparous, and aged under 20, delivering a female infant vaginally. Evidence from the five centres suggested that hospital staff have little influence on a mother's choice of feeding method. The major differences between the populations of babies whose mothers do or do not choose to provide milk, raise important issues concerning the interpretation of data from non-randomised clinical trials of feeding premature infants.

Does it matter how we feed premature babies?

The multiplicity of dietary regimes available for low birthweight infants is a measure of clinical uncertainty in this field. The reasons for this persisting uncertainty are analysed: few studies have examined whether early diet matters in terms of clinical outcome; instead, management decisions have been based on short-term 'physiological' studies on nutrient accretion, growth and metabolism. Data from this Unit's multicentre outcome trials on nearly 1000 preterm infants, randomly assigned to early diet, are used to demonstrate that whilst diet influences many aspects of the infants 'physiology' in the short term, such physiological responses have limited value in predicting clinical outcome. Preliminary data from the early follow-up of this cohort to 18 months post-term suggest that the diet used in the neonatal period may have persisting consequences in terms of motor and mental development and growth. The longer-term significance of these findings is being investigated.

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Assessment of proportional growth of very low birth weight infants fed banked human milk

Twenty appropriate (mean +/- S.D., gestational age (AGA): 29.9 +/- 1.5 weeks) and 15 small (GA: 34.6 +/- 2.4 weeks) for gestational age (SGA) very low birth weight infants fed banked mature human milk were studied until term for anthropometric parameters: midarm (MAC), chest (CC), head (HC) circumferences, triceps (TSKF) and subscapular (SSKF) skinfold thickness recorded at 15 and 60 s, dynamic skinfold (delta % SKF), muscle (AMA) and fat (AFA) areas, weight and length. In AGA infants, all the parameters at term were significantly lower in extrauterine (EUL) that in intrauterine life (IUL). At term the relative proportion of AFA to total arm area was increased in EUL compared to IUL both in AGA (25.87 +/- 3.8 vs. 23.26 +/- 1.27% respectively, P less than 0.01) and in SGA infants (21.89 +/- 4.63 vs. 18.81 +/- 3.9 respectively, P less than 0.05). SGA infants showed a similar growth in EUL compared to IUL, and a significantly lower AMA and AFA than in AGA infants in EUL. Although HC was in both infants below the 10th centile at term, the ratio weight/HC2 suggests a relative preservation of head growth in EUL compared to IUL (AGA: 20.72 less than 0.87 vs. 22.65 +/- 1.46 respectively, P less than 0.001; SGA; 20.82 +/- 1.16 vs. 21.62 +/- 1.86 respectively, NS). Delta %SKF were negatively correlated with post-conceptional age suggesting a loss of extracellular water in AGA (delta %TSKF: r = -0.287, P less than 0.02) and in SGA infants (delta %TSKF: r = -0.301, P less than 0.02; delta %SSKF: r = -0.316, P less than 0.02). An intrauterine model of discrimination between AGA and SGA infants does not apply to EUL. An equation was established in SGA infants with the best discriminant parameters giving a predictive post-conceptional age: post-conceptual age (PCA) (weeks) = 0.276 HC (cm) + 0.723 CC (cm) - 0.122 MAC (cm) + 0.5 TSKF (mm) + 10.173, (r = 0.867, P less than 0.001) allowing a clear discrimination between AGA and SGA infants. These results suggest that infants show quite different growth patterns between IUL and EUL both for AGA and SGA infants.

Breast milk jaundice in premature infants

In randomised study of 186 preterm infants those fed on maternal or banked breast milk had a significantly higher peak bilirubin concentration and a more prolonged jaundice than infants fed an artificial preterm formula and were over four times more likely to achieve plasma bilirubin values above 200 mumol/l (11.7 mg/100 ml). This dietary effect was seen even in a high risk subgroup of sick ventilated infants below 1500 g who were receiving restricted enteral intakes. We suggest that breast milk jaundice in preterm infants may increase clinical intervention. Our findings are discussed in the light of epidemiological data suggesting an association between moderate hyperbilirubinaemia (greater than 170 mumol/l) and neurodevelopmental outcome.

A comparative study of a premature infant formula and preterm breast milk for low birthweight infants

Although the unique composition of preterm milk (PTM) has led to its increasing use in feeding of low birthweight (LBW) infants, controversy exists as to whether such milk adequately meets their requirements. This study compares the clinical tolerance and anthropometric, biochemical and haematological parameters of LBW infants fed exclusively with their own mother's PTM, a premature infant formula (Alprem; Nestlé Australia) and a mixture of PTM and Alprem. Of 90 enrolled LBW infants (1000-1750 g birthweight), 78 completed the feeding trial for a mean duration of 42 days. Twenty-eight babies were fed Alprem (Group A), 31 received a mixture of Alprem and PTM (Group B) and 18 received PTM (Group C). Babies in Groups A and B were smaller, less mature and more asphyxiated at birth than those in Group C. Weight gain from full enteral feeding was greater in Group A (18.1 g/kg per day) and Group B (17.6 g/kg per day) than in Group C (13.0 g/kg per day). Throughout the trial, weight gain in Groups A and B exceeded predicted intra-uterine growth rates, whereas that for Group C approximated the predicted intra-uterine growth rates. Growth rates of length and head circumference were also greatest in the Alprem-fed babies. Infants receiving PTM were supplemented with calcium, sodium, vitamins and energy, whereas the only three infants requiring mineral supplementation in the Alprem group were those receiving Frusemide therapy for chronic lung disease. lower serum concentrations of phosphorus, iron, albumin and urea, and higher zinc and alkaline phosphatase concentrations were found in infants receiving PTM (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal growth in infants born before 30 weeks' gestation

The postnatal weight pattern up to 14 weeks after birth was determined in 184 singleton survivors born at 23 to 29 weeks' gestation in whom routine parenteral nutrition was used before milk feeding was established. A mean postnatal weight loss of 14% of birth weight occurred at a mean of 6 days. The more immature infants had significantly higher postnatal weight loss and longer time to regain birth weight despite a higher volume intake in the first week. From the fourth postnatal week all gestational subgroups had a mean weight gain at above intrauterine growth rate. As a result of the initial period of weight loss, however, the mean body weight remained below the 10th percentile of the intrauterine growth curve. The early growth rate in infants small for gestational age was higher than those who were appropriate weight for gestation, although the mean body weight of the former group remained significantly lower at 2 years.

Evaluation of a special low birth weight formula, with and without the use of medium chain triacylglycerols

A special low birth weight formula containing 1.8 g/100 ml of medium chain triacylglycerols (Nenatal) was compared with 'modified' Nenatal (medium chain triacylglycerols (MCT) replaced by long chain triacylglycerols (LCT)) and standard modified baby milk (Cow and Gate Premium). 22 infants of birth weight less than 1500 g and gestational age less than 33 weeks were studied for three weeks when enteral feeds were well tolerated. Nenatal was given to all infants for the first and third weeks, during the middle week 11 infants received Premium and 11 infants received modified Nenatal. On Nenatal there was a significant elevation of serum beta-hydroxybutyrate and small amounts of medium chain fatty acids were detected in the serum. Glucose and long chain triacylglycerol levels were similar on all feeds. Incremental weight gain and energetic efficiency of weight gain was significantly greater on Nenatal than on Premium, but there was no difference in this respect between Nenatal and modified Nenatal. We conclude that the use of a special low birth weight formula is associated with increased weight gain, but this is not dependent on the presence of MCT in the feed. Therefore although feeds containing MCT are well tolerated, there seems little advantage in including MCT in the formulation of low birth weight feeds.

The effects of two extremes of dietary intake on protein accretion in preterm infants

A comparison has been made of protein accretion and growth in premature infants fed banked drip breast milk (BBM) or a preterm formula (PF). Protein accretion was calculated from the difference between dietary nitrogen intake and output in urine and stools, measured in a nutrient balance study. As expected, only the infants fed PF achieved the intrauterine growth rate. However, whilst weight gain in infants fed BBM was 71% of that in the group fed PF, the rate of protein deposition was less than 50%. As a result, the protein concentration in new tissue of infants fed BBM averaged 32% less than in those fed PF and 21% less than the lower end of the range reported to occur in utero. We speculate that infants fed BBM have an abnormally low protein concentration in their lean body mass.