High versus low medium chain triglyceride content of formula for promoting short term growth of preterm infants

In-hospital growth of most very low birth weight infants remains below the 10th percentile of reference intrauterine growth curves (Ehrenkranz 1999). To improve growth, fat is added to preterm formula in the form of medium chain triglycerides (MCT) or long chain triglycerides (LCT). MCT are easily accessible to the preterm infant with an immature digestive system while LCT are important in the development of the retina and visual acuity. Both have been incorporated into preterm formulas in varying amounts, but their effect on the preterm infant's short term growth is unclear.

To determine among preterm, formula fed infants, does high MCT as opposed to low MCT (high LCT) formula promote higher short term growth rates.

MEDLINE (1966-2002), CINAHL (1982-2002), Cochrane Controlled Trials Register (The Cochrane Library, Issue 4, 2001), conference proceedings, and reference lists of articles were searched.

All randomized trials comparing the effects of exclusive feeding of high versus low MCT formula (for a minimum of one week) on the short term growth of healthy, preterm infants.

Two reviewers assessed each study's quality and extracted data on growth parameters as well as adverse effects from included studies. All data used in analysis were continuous, and therefore weighted mean differences with 95% confidence intervals were reported.

Eight randomized trials studying a total of 182 infants were included. There was no evidence of difference in short term growth parameters when high and low MCT formulas were compared. The meta-analysis of weight gain based on five studies yielded a WMD of -0.35 g/kg/d (95% CI -1.44, 0.74). Similarly, meta-analysis of weight gain in g/d based on two studies showed no evidence of difference (WMD 2.09 g/d, 95% CI -1.46, 5.64). Length gain, based on five studies, showed a non-significant WMD of 0.14 cm/wk (95% CI -0.04, 0.31). Head circumference gain, based on data from five studies, showed a non-significant WMD -0.03 cm/wk (95% CI -0.15, 0.08). Only one study reported skin fold thickness gain, with a mean difference -0.15 mm/wk (95% CI -0.41, 0.11), again not significant. Subgroup analyses according to % MCT in the high MCT formula, by 10% intervals, showed no evidence of effect of high MCT on short term weight gain within any subgroup. There are conflicting data (two studies) as to formula tolerance. There is no evidence of effect on incidence of necrotizing enterocolitis (NEC), based on small numbers in two trials. No studies were located addressing long term growth parameters or neurodevelopmental outcomes.

There is no evidence of difference between MCT and LCT on short term growth, gastrointestinal intolerance, or necrotizing enterocolitis. Therefore, neither formula type could be concluded to improve short term growth or have less adverse effects. Further studies are necessary because the results from the included eight studies are imprecise due to small numbers and do not address important long term outcomes. Additional research should aim to clarify effects on formula tolerance and on long term growth and neurodevelopmental outcomes, and include larger study populations to better evaluate effect on NEC incidence.