Each year, around 1 in 10 infants are born prematurely and require extra care and nutrition to support proper growth [1]. Complications due to preterm birth are among the leading causes of mortality in children under 5 globally; these problems can include restricted growth and impaired metabolic processes [1]. Understanding the impact of preterm birth on the metabolic development of infants is essential to inform optimum nutritional support as they age. Through the use of metabolomic analysis, we aim to gain insight into changes occurring in preterm infants as they age.

In this study, urine samples were collected from 54 preterm infants with birth gestational ages ranging from 23 to 31 weeks. These infants were sampled from birth and up to week 18 of life. Nuclear magnetic resonance (NMR) spectroscopy was used to measure the metabolic profiles of these samples. Projection to latent structures (PLS) models were used to identify metabolites associated with gestational age and growth, defined as change in weight-for-age z-score between birth and discharge. Metabolites of interest were subsequently investigated in vitro by treating C₂C₁₂ myotubes. Morphological analysing and gas chromatography-mass spectrometry (GC-MS) was used to assess the effects of metabolite treatment on muscle growth and metabolism.

Metabolites linked to a greater gestational age were involved in energy metabolism, namely the TCA cycle (citrate and succinate), muscle growth (valine) and choline metabolism (betaine and DMG). Higher excretion of glucose was associated with lower gestational age, which decreased over the first months of life (Q²Y = 0.236, p = 0.001). Citrate excretion was also associated with better growth and was increased when infants were provided with greater amounts of certain nutrients, including choline, fat and carnitine (Q²Y = 0.22, p = 0.001). In addition to this, betaine treatment in vitro increased myotube diameter (control mean = 14.7 ± 1.98 SD , betaine treatment mean = 15.8 ± 2.27 SD) and altered the metabolome.

The findings highlight urinary biomarkers that can predict growth outcomes in preterm infants and guide nutritional support. Specifically, citrate was associated with greater growth and could be increased with nutritional intake in preterm infants. Glucose may be another biomarker to investigate further as it is commonly measured in the clinic and could be viably monitored to assess biochemical maturation in these infants. Betaine was associated with greater gestational age and an increase in myotube diameter, so may be helpful for muscle growth. These results indicate metabolic processes that may be dysregulated in preterm infants contributing to poor growth and highlight pathways of interest for further research.