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Re: Preterm weaning strategy-is it beneficial in the longer term?

Dear Editor

I read with interest the article on weaning preterm infants by Marriott et al.[1] Authors of this article deserve congratulations for conducting randomised controlled trial in an area with sparsity of evidence and little research. The preterm weaning strategy (PWS) adopted in this study showed benefits in terms of improved length growth velocity between 0 and 12 months corrected gestational age (CGA). This study also demonstrated improved intake of energy, protein and carbohydrate at 6 months and iron at 12 months CGA. However, I would like to make following comments, which need clarification.

Firstly, the mean gestational age of infants included in this study is 31-32 weeks. Hence, this study has not looked at the most disadvantaged group of extreme preterm infants (with birth weight < 1 kg and < 28 weeks gestation). It would be very interesting to see the effects of similar PWS in extreme preterm infants, which may require a multi center trial.

Secondly, study subjects were only followed up to 1 year of age. Their follow up showed that the beneficial effects of increased energy, protein and carbohydrate intake at 6 months CGA had already been lost by 12 months CGA with no significant difference between the two groups. More over, although dietary intake of iron was significantly higher in the intervention group at 12 months, this was not supported by haemoglobin, serum ferritin and serum iron levels at 12 months CGA. It would have been useful to look at the effects of PWS on the development at 6 and 12 months of age.

Authors mention that significantly higher number of infants (29) in the PWS group were given breast milk fortifier compared with 16 in control group (p = 0.02). Additionally, authors compared only 16 infants in the control group versus 27 in the PWS group at term (0 month CGA). I wonder if these factors might have influenced the comparison of daily intakes of energy, macronutrients and iron at term in the two groups.

There is evidence to support that preterm infants have special nutritional requirements in the post discharge period due to number of reasons including smaller size, reduced body stores of nutrients, undermineralised bones, accumulated energy deficits and higher nutrient requirements. A number of studies have looked at different randomized diets (in preterm infants) in the neonatal period and their effects on growth performance and bone mineralization in the longer term showing that early diet had no influence on weight, height, head circumference or skin fold thickness at 7.5-8 years [2] and does not effect the bone mass in preterm infants at 8-12 years.[3] However, Lucas et al have exhibited the beneficial effects of nutrient enriched discharge formula (with higher protein to energy ratio) in preterm infants by demonstrating improved verbal intelligence quotient scores at 7.5-8 years of age.[4] It would be intriguing to follow up this cohort well into the childhood to see the beneficial effects of PWS especially in terms of growth, development and intelligence quotient.

References

(1) Marriott LD, Foote KD, Bishop JA, Kimber AC and Morgan JB Weaning preterm infants: a randomised controlled trial Arch Dis Child Fetal Neonatal Ed 2003;88:F302-F307.

(2) Morley R and Lucas A Randomized diet in the neonatal period and growth performance until 7.5-8 years of age in preterm children. Am J Clin Nutr 2000;71:822-828

(3) Fewtrell MS, Prentice A, Jones SC, Bishop NJ, Stirling D, Buffenstein R, Lunt M, Cole TJ and Lucas A Bone mineralization and turnover in preterm infants at 8-12 years of age: The effect of early diet. J Bone Miner Res 1999;14:810-820.

(4) Lucas A, Morley R and Cole TJ Randomised trial of early diet in babies and later intelligence quotient. BMJ 1998;317:1481-1487.

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Re: Authors' reply to Dr Ahmed

Dear Editor

We thank Dr Ahmed for his kind comments about our study.[1] We are happy to provide the additional clarification he requests.

Firstly, we included 9 babies with a birth weight less than 1.0 kg and 14 babies of gestational age less than 28 weeks in the study, equally distributed between the intervention and control groups. We agree that it would be interesting to repeat the research in an extremely low birth weight sub group but as stated by Dr Ahmed a large multi-centre study would be needed.

Secondly, by 12 months gestation corrected age (GCA) the intakes of energy, protein and carbohydrate were no longer statistically significantly greater in the intervention group than in the control group. However, even in this small study, at 12 months GCA iron intakes were significantly higher and the percentage of babies using cow's milk as their main drink significantly lower as a result of the preterm weaning strategy. We would have liked to have carried out further estimates of haemoglobin, ferritin and iron status at 12 months GCA but were constrained from performing a third blood test for a mixture of financial, practical and ethical reasons.

Thirdly, there were no statistical effects at term, 6 months GCA or 12 months GCA on dietary intakes, growth or iron status of breast milk fortifier. We could only determine dietary intakes accurately, at term, for those infants who were not breastfed. However, as the nutritional intervention did not commence until after term, this gave us a 'base-line' dietary intake determination.

Growth and neurodevelopmental assessments of our subjects carried out at 18 months and 36 months GCA have been completed and will be submitted for publication in the near future.

We hope this information fully answers Dr Ahmed's queries.

Reference

(1) Ahmed M. Preterm weaning strategy-is it beneficial in the longer term? [electronic response to Marriott et al. Weaning preterm infants: a randomised controlled trial] archdischild.com 2003 http://adc.bmjjournals.com/cgi/eletters/fetalneonatal;88/4/F302#214