Late Preterm Infant Growth and Body Composition at Corrected Term Gestation: A Cohort Study

Abstract

Introduction: Worldwide major proportion of preterm births is late preterm infants. Preterm infants are deprived of optimal in-utero nutrition leading to immediate consequences of growth failure and long-term complications like adverse neurodevelopment outcomes whereas preterm infants with fast catch up growth after birth have health consequences like obesity and hypertension in adulthood. Aim: To assess growth of late preterm infants at their term equivalent Gestational Age (GA) and compare their growth and body composition with term infants. Materials and Methods: This was a cohort study of late preterm (34 0/7 to 36 6/7 weeks) infants that were Appropriate for Gestational Age (AGA) and controls that were AGA term infants (39 0/7 to 40 6/7 weeks). All enrolled late preterm infants were followed-up at term equivalent (39 0/7 to 40 6/7 weeks). Growth plotted on Fenton’s chart and body composition were calculated using pre-defined formula for total mid-upper arm area (cm2), mid-upper arm muscle area (cm2), mid-upper arm fat area (cm2), and the Arm Fat Index (AFI) (%). The data was analysed using Epi info (version 7.2) with student t-test for continuous variables and chi-square test for dichotomous variables. A p-value of <0.05 was considered statistically significant. Results: Out of the 135 infants enrolled, 45 were late preterm and 90 were term born infants. Median GA of the case cohort was 35 (IQR 35-36) weeks and in the control cohort it was 39 (IQR 39-40) weeks. Total 45.7% (N=35) of the late preterm infants (after excluding loss to follow-up) were below 10th percentile (EUGR) at term GA. At term follow-up, mean weight and length of late preterm infants compared to term born infants was less and statistically significant. The mean Skin Fold Thickness (SKT) (cm) at triceps level 0.55 (SD 0.07) vs. 0.49 (SD 0.06), mean of calculated AFI (%) 31.25 (SD 3.08) vs. 28.19 (SD 2.5) and among late preterm infants at follow-up was more than in term infants and was statistically significant. Conclusion: Failure to thrive is common among the late preterm infants at term equivalent GA. Late preterm infants show postnatal growth characterised by predominant fat mass accretion and less lean mass.