Body composition in very preterm infants during their hospital stay

Abstract

Background The survival of preterm infants has increased over the past decades. However, these infants are still at high risk of poor growth especially those born at <32weeks gestation (very preterm infants, VPT infants). The American Academy of Paediatrics recommends that the “postnatal growth of preterm infants in both their anthropometric indices and body composition should be the same as the normal fetus of the same gestational age”. VPT infants at term equivalent age have been reported to have an increased percent body fat (%FM) and a lower fat free mass (FFM) when compared with term born infants. Nutritional and non-nutritional interventions during this period before term equivalent age have been closely associated with later growth but also with important neurodevelopmental and metabolic outcomes. Few studies in VPT infants have reported body compositional changes during their hospital stay and before term equivalent age. Aim The aim of this thesis is to assess growth and body composition, and to examine the nutritional and non-nutritional predictors of these, in VPT infants during their hospital stay. Methods Growth and body composition were assessed using air displacement plethysmography (PEAPOD) to measure %FM and FFM (g) in infants (n=113) born before 32wks gestation and studied at 32-36wks post menstrual age (Study Infants). Study infants were compared to a second group of preterm infants (n=88) born at 32-36wks gestation who were measured at two to five days post-partum, representing in-utero growth (Control group). Anthropometric measures for all infants included weight, length, head circumference, abdominal circumference and mid upper arm circumference. Actual macronutrient intakes of protein, lipid, carbohydrate and energy were calculated in VPT infants from birth until 34 weeks post menstrual age from the daily fluid records of parenteral and enteral intake. Infant morbidities and maternal characteristics were derived from infant and maternal medical records and examined for their effect on VPT infant body composition and growth. A %FM prediction equation for VPT infants was developed from the anthropometric measurements. Results %FM in study infants at 32-36 weeks PMA was significantly higher than that in control infants born at 32-36 wk (p<0.0001). The mean FFM (g) in VPT infants was significantly lower than the mean FFM in control infants (p <0.001). The mean protein intake from birth to 34wks PMA (2.4 g/kg/day ± 0.4) did not meet the intake recommended by the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) of 3.5-4.5 g/kg/day. Total energy (112 kcal/kg/day), lipid (5.2 g/kg/day) and carbohydrate (13.8 g/ kg/day) intakes from birth to 34 wks PMA did meet the ESPGHAN guidelines, however, no macronutrient reached the recommended level before 14 days after birth. The %FM of VPT study infants was most closely associated with PNA and not significantly associated with individual nutrient intake after the first three days from birth. There was a negative association between early protein, fat and energy intake and absolute fat mass (FM) at 3236 weeks. The FFM of these VPT infants was most closely associated with PMA but a significant association with individual macronutrients at the range of exposure in this cohort was not found. Gestational diabetes appears to influence body composition in very preterm infants measured at 32-36 weeks PMA. The best model using anthropometric measurements to predict %FM in these VPT infants was 1.07 PNA + 1.71 MUAC+ 0.25 weight velocity – 9.25. Conclusions Preterm infants accumulate fat rapidly soon after birth and this appears to be triggered by birth. This drive to accumulate fat appears to be intensified when nutrient intake, particularly protein, is low. Low nutrient intakes in the first week after birth have the strongest influence on fat accumulation and thus early administration of protein and fat may reduce fat accumulation in VPT infants. Monitoring of body composition rather than assessment solely by weight gain is important, and is feasible in VPT infants as early as 32 weeks postmenstrual age by using Air Displacement Plethysmography (ADP). In the absence of ADP, an innovative %FM prediction equation using anthropometric measurements could be used in VPT infants.