Growth in preterm infants until 36 weeks' postmenstrual age is close to target recommendations.

Objective: To establish the determinants of weight, length and head circumference changes during their initial hospitalization in very-low-birth-weight preterm infants.

Subjects/methods: A prospective cohort study was performed. Weight z-score and percentage of target dietary intakes (TDIs) were prospectively determined daily during the first 5 weeks of life in a group of preterm infants (n = 111, birth weight <1,500 g, gestational age <34 weeks). Weight, length and head circumference at 36 weeks' postmenstrual age (PMA) were recorded. A mixed effects regression model was used to evaluate changes in weight z-score during the first 5 weeks of life. Simple Pearson correlations and stepwise logistic regression were used to determine the relationship between fetal growth, illness severity, nutritional intake and growth at 36 weeks' PMA.

Results: Weight z-score decreased significantly in all infants during the first 5 weeks of life from -0.92 ± 0.66 at birth to -1.89 ± 0.65 at 5 weeks. The variation of weight z-score during the first 5 weeks of life was influenced by weight z-score at birth, energy and protein intakes and gestational age. Mean energy and protein intakes were 95.5 and 86.4% of TDIs. Weight z-score fell to -2.05 ± 0.64 at 36 weeks' PMA. Birth weight z-score was significantly correlated with weight z-score at 36 weeks (R2 = 0.71; p < 0.001). Severity of illness influenced the weight z-score at 36 weeks.

Conclusion: Despite achieving a protein and energy intake close to the described target intake, the rate of growth in our infants was lower than indicated by the intrauterine growth curve. Lower gestational age, lower birth weight and severe illness had a negative effect on growth.