No abstract

Objective-A prospective, cross-sectional, observational study in pre-and term infants was performed to compare multimodal measurements of body composition namely, limb ultrasound, bone quantitative ultrasound and dual X-ray absorptiometry (DXA).Patients and Methods-102 preterm and term appropriate for gestational age infants were enrolled from the newborn nursery and neonatal intensive care unit. Infants were included when they were medically stable, in an open crib, on full enteral feeds and within one week of anticipated discharge. Correlations among the various measurements of body composition were performed using standard techniques. A comparison between preterm infant (born at 28-32w) reaching term to term born infants was performed.Results and Conclusions-Limb ultrasound estimates of cross sectional areas of lean and fat tissue in a region of tissue (i.e., the leg) were remarkably correlated with regional and whole body estimates of fat free mass and fat obtained from DXA suggesting the potential usefulness of muscle ultrasound as an investigative tool for studying aspects of body composition in this fragile population. There was a weak but significant correlation between quantitative ultrasound measurements of bone strength and DXA derived BMD. Preterm infants reaching term had significantly lower body weight, length, head circumference, muscle and fat cross sectional area, bone SOS, whole body and regional lean body mass, fat mass and BMD compared to term born infants. Current post-natal care and nutritional support in preterm infants is still unable to match the in-utero environment for optimal growth and bone development. The use of relatively simple bedside, non invasive body composition measurements may assist in the understanding how changes in different components of body composition early in life affect later growth and development.

Little is understood about the optimal balance between IGF-I and antagonistic inflammatory mediators, such as IL-6, in growing preterm infants. Using a prospective cohort study, we investigated the relationship between postnatal growth of preterm infants and key growth and inflammatory mediators. We studied 51 stable, growing preterm infants (mean gestational age: 27.8 +/- 0.4 weeks, mean birth weight: 1,032.8 +/- 50.6 g). IL-6 and IL-1ra (reflecting stress/ inflammation) and IGF-I and GHBP (reflecting anabolic activity and GH sensitivity) were measured at enrollment and discharge using ELISA. During the observation period (mean 6.1 +/- 0.34 weeks) there was a significant increase in weight (1,396 +/- 81 g, p < 0.0001). IGF-I increased from 46.6 +/- 4.1 to 88.7 +/- 5.2 ng/ml (p < 0.001). In contrast, IL-6 decreased from 9.5 +/- 1.0 to 2.3 +/- 0.34 pg/ml (p <0.001) and IL-1ra from 6,042 +/- 362 to 4,851 +/- 365 ng/ml (p = 0.007). GHBP increased from 65.8 +/- 6.7 to 82.5 +/- 7.9 ng/ml (p = 0.003). IL-6 was inversely correlated with IGF-I (p < 0.001). In addition, a multiple regression model showed IGF-I levels correlated positively and IL-6 levels inversely with various parameters of growth. Growth in preterm infants is characterized by increases in IGF-I and GHBP with simultaneous decreases in IL-6 and IL-1ra. Efforts to optimally balance inflammatory and growth mediators may benefit somatic growth in infants very early in life.

Preterm infants with lower bone SOS at birth tend to 'catch-up' during early postnatal weeks. Increases in bone strength in preterm infants were associated with reduced inflammatory state as suggested by lower levels of circulating IL-6.