Year: 2019
Type: dissertation
Study design: Observational Study
Abstract: With a growing body of evidence suggesting that growth during infancy and early childhood is associated with later life morbidity, research on early life growth is critical. Preterm infants, an often-understudied population in terms of growth, are exposed to numerous perinatal risk factors for poor growth outcomes. In addition to the complications associated with prematurity, preterm infants have major risk factors for abnormalities in growth and weight, including low birth weights and rapid postnatal catch-up growth. With the clinical abnormalities and risk factors observed in preterm infants and the increasing rate of preterm birth, research on growth in this unique, at-risk population is crucial. However, previous research investigating growth in preterm infants, and the factors that influence their growth, is lacking. Data from the Iowa Perinatal Health Research Collaborative (IPHRC) were utilized to address three aims: 1) examine the effects of perinatal and early life factors on the growth trajectories of children born preterm, 2) define the impact of additional nutritional support, in the form of total parenteral nutrition (TPN), at birth on later life physical growth in children born moderately preterm, and 3) determine if neonatal glycemic status in moderate and late preterm infants is associated with postnatal growth outcomes. First, perinatal determinants of early life growth trajectories were examined in all preterm infants. Linear mixed modeling, with random slopes and intercepts, was employed to estimate (z-weight) growth trajectories. Factors found to influence growth over time in children born at term, such as maternal race and gestational age, were also found to affect growth of preterm infants. Interestingly, factors that occur at higher frequency in preterm infants also exert significant influence on growth rates. The strength of association and the magnitude of effects varied by gestational age, revealing that significant heterogeneity in growth and its determinants exists within the preterm population. To accurately study the impact of TPN on weight z-score at six months corrected age in children born moderately preterm, machine learning approaches were used to generate propensity scores for inverse probability of treatment weighted regression. TPN was significantly associated with z-weight at six months corrected age, resulting in an average reduction of z-weight score by 0.39 in the population. While this reduction in weight seems counterintuitive given previous investigations in other populations, the effect is compared to those who did not receive this form of nutrition, who had higher z-weight scores at six months of age. Thus, on average, receiving TPN was associated with z-weight scores that were closer to the median, optimal weight-for-age. Overall, this finding warrants further study of TPN on long-term growth and adiposity measures in children born moderately preterm. Finally, a retrospective cohort study was utilized to examine the relationship between neonatal blood glucose levels in the first day of life and postnatal growth in children born moderately to late preterm. Debate exists regarding appropriate definitions for abnormal neonatal blood glucose levels, largely due to the lack of evidence regarding the levels at which glucose causes long-term adverse outcomes. As such, neonatal blood glucose was defined in multiple ways to determine if variability, commonly used clinical definitions, or median glucose levels are causally related to long-term growth outcomes. The association between neonatal blood glucose levels in the first day of life with z-weight score at six months corrected age varied based on categorization of glucose and the degree of prematurity. This provides additional evidence that, while glucose levels are associated with neonatal growth, the exact definition of glucose levels in neonates, particularly those born preterm, should be carefully considered in both research and clinical practice. Early life growth has important consequences later in life, with abnormalities in growth during the early postnatal period tied to increased mortality and morbidity. This research fills a critical gap in knowledge by focusing on the vulnerable, understudied population of children born preterm. Understanding the factors influencing growth in preterm infants is important, as modification of these processes in early life could have lasting effects on an individuals’ health from infancy to adulthood. Overall, these findings demonstrate a need for further research and interventions targeting preterm infants in the perinatal periods.
DOI: 10.17077/etd.005198
Language: English
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W4239132217