The length of human pregnancy, arguably the most natural of physiological processes, is undergoing subtle but consequential modification in order to adapt to modern societal demands. The gestational age distribution of births in the United States has been shifting to lower gestational ages over the past two decades, parallel to a concomitant rise in obstetrical intervention in pregnancy. The result has been an increase in elective deliveries at 37-38 weeks (early term). A population-based retrospective cohort study of over 616,000 live-born full-term singleton infants was conducted to investigate the association between elective early term delivery and subsequent infant morbidity, mortality, and health care utilization in the first year of life. Data were examined from a statewide, multi-year, clinically-enhanced database created by linking birth certificate records to maternal and infant hospital discharge records, and to infant death certificates, for all infants born to Florida-resident mothers from 2005-09. All infants delivered to mothers with an established medical condition that could have justified early delivery were excluded from the study, as it would not be possible to determine if an early delivery in those cases was elective or medically-necessary. Based on the timing and reason for delivery initiation, the study population was categorized into four exposure groups: 1) early electively induced delivery at 37-38 weeks (EED-I), 2) early elective cesarean delivery at 37-38 weeks (EED-CS), 3) early spontaneous delivery at 37-38 weeks (ESD), 4) early medically-indicated delivery at 37-38 weeks (EID). The comparison group consisted of all expectantly managed infants who were full term deliveries (FTD) at ≥39 weeks. Adverse infant outcomes in the first year of life included respiratory morbidities, neonatal sepsis, feeding difficulties, admission to the neonatal intensive care unit, the frequency and duration of hospital encounters, and infant mortality. Multivariable generalized linear mixed models were used to estimate odds ratios (OR) or rate ratios (RR) and 95% confidence intervals (CI) between exposure and each outcome, adjusting for maternal, infant, and hospital characteristics and accounting for the correlation among infants born at the same facility. Infants who were delivered by EED-I or EED-CS comprised 13% of the study population, and 40% of infants born in the early term period. Infants who were delivered by EED-I experienced the lowest likelihoods of respiratory morbidities, neonatal sepsis, and admission to the NICU when compared to FTD infants. In contrast, infants delivered by EED-CS had significantly increased risks several adverse birth outcomes, with magnitudes ranging from a 9% to 40% increase. Only 8.3% of all infants were re-admitted to the hospital after birth. Despite having the lowest likelihood of the birth morbidities studied, infants delivered by EED-I had a small 10-15% increased odds of being re-hospitalized in the first year of life, compared to FTD infants. These infants also had a slightly higher mean number of visits and combined LOS during post-birth hospitalizations, although the absolute differences from other exposure groups was small. Elective early term cesarean infants actually had a slightly lower risk of re-hospitalization, particularly re-hospitalizations that occurred between weeks 3-52 of life. Neonatal and post-neonatal deaths were rare events (0.3 and 1.3 deaths per 1,000 live births, respectively) in this comparatively low-risk study population. There were no differences in survival when comparing the EED-I and EED-CS groups to the FTD group. The results of this study raise the concern that these public health efforts to reduce elective early term inductions have been based on biased evidence from a limited number of studies in which artificially elevated risks for early electively-induced infants were reported. In stark contrast to the current dogma, this study found that when a methodologically appropriate comparison group was used (i.e., expectant management), elective induction prior to 39 weeks was NOT associated with an increased risk of any adverse infant outcomes in early life. In contrast, our findings do support the avoidance of purely elective cesarean sections prior to 39 weeks in lieu of expectant management. The evidence presented in this large, methodologically-sound study should caution against a general avoidance of ALL elective early term deliveries, and foster support for continued research in this still relatively new arena.

Objectives: Infants delivered at ≥37 weeks’ gestation are considered full term, but research has demonstrated those born at 37 to 38 weeks (early term) have a higher risk for poor birth outcomes than deliveries at 39 to 41 weeks (full term). Despite this, many deliveries occur electively (scheduled, no medical indication) before 39 weeks. This study examined the risks of elective early-term delivery in a disadvantaged, rural sample and compared these results with national findings. Methods: Data were available for 638 rural women, recruited prenatally from three counties in rural southern Appalachia, who delivered electively at ≥37 weeks. Results: Compared with electively delivered full-term infants, those delivered electively at early term were 7.7 times more likely to be low birth weight, 4.4 times more likely to have a neonatal intensive care unit admission, and 2.5 times more likely to develop jaundice. Those living furthest from the hospital were most likely to deliver electively at <39 weeks. Although rates of elective deliveries <39 weeks were no higher than national rates, adjusted odds ratios (aOR) of associated admission to a neonatal intensive care unit doubled (aOR 4.4 vs aOR 2.2). Conclusions: Results demonstrate that initiatives targeting early-term elective deliveries are needed in rural, disadvantaged regions.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), a keystone species in western Washington, faces threats on plantations across this region from the invasive species Scotch broom (Cytisus scoparius (L.) Link), whose invasions on recently established stands can lead to mortality of Douglas-fir through overtopping. The susceptibility of sites to Scotch broom achieving dominance over Douglas-fir has been demonstrated as highly site dependent, however the site conditions that cause this have not yet been identified. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This thesis strives to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what factors improved growth of Douglas-fir during the period when they are at the greatest risk, and second, identifying factors that led to Douglas-fir outcompeting Scotch broom on sites they cohabitated. In Chapter 1, we utilized LiDAR scans, Soil Survey Geographic Database characteristics, and management histories to identify conditions that improved growth for Douglas-fir in ages 3-8. Individual tree detection was used to measure Douglas-fir heights, and a correction algorithm for LiDAR measured young Douglas-fir heights was established from field validation data. We identified that young Douglas-fir had improved growth on sites with lower elevation, flatter slopes, and finer textured soils. The factors identified were then transformed into four potential site index models based on mean stand elevation class, Mean stand elevation class and clay class, textural class and slope class, and textural class and Mean stand elevation class. In Chapter 2, we used paired field plots to examine Douglas-fir and Scotch broom competition on 19 sites across western Washington. Each site had 2 plots with only Douglas-fir and 2 plots with Douglas-fir and Scotch broom. Elevation, soil texture, and soil nutrient composition for carbon, nitrogen and available phosphorous were examined for influence on height and growth rate of both species. We identified that Scotch broom presence was negatively related to Douglas-fir height growth and that sites with either higher percentages of silt, lower concentrations of phosphorous, or higher percentages of Carbon were more likely to have growth patterns close to or exceeding Scotch broom. / Master of Science / Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) is a valuable timber species across western Washington that is commonly grown in plantations. In western Washington when Douglas-fir are planted on a site they often face competition from the invasive shrub Scotch broom (Cytisus scoparius (L.) Link). When Scotch broom invasions occur on a recently planted Douglas-fir stands, they can cause death of the trees if Scotch broom plants grow taller than the young Douglas-fir and obstruct their access to light, a process called overtopping. The risk of Douglas-fir being overtopped has been shown to be dependent on location, however what causes a location to be at risk of overtopping is yet unknown. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This study aims to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what sites generate the best Douglas-fir growth when they are young and at risk of being overtopped, and second, identifying site characteristics led to Scotch broom growing faster than Douglas-fir on sites they both occur on. To identify sites that produced greater young Douglas-fir height growth we used publicly available soil data from the Soil Survey Geographic Database and company management histories to predict tree heights measured through aerial laser scanning (LiDAR). We found that sites with soil textures that had higher percentages of smaller particles, were on lower elevations, and had gentler hillslopes could all produce greater Douglas-fir height growth. When attempting to identify what causes Douglas-fir to be at risk of being overtopped by Scotch broom we used plots with and without Scotch broom on a variety of field sites. This allowed us to not only identify which characteristics of sites where Douglas-fir was being outgrown by Scotch broom, but also identify if Scotch broom was changing how Douglas-fir grew. We found that reductions in Douglas-fir growth were related to Scotch broom being present and that increases in soil silt percentages, decreases in soil phosphorus concentrations, and increases in soil carbon percentages were related to Douglas-fir having height growth closer to or exceeding that of scotch broom.

La prématurité, définie par une naissance avant 37 semaines d’aménorrhées (SA), est une cause majeur de mortalité et de morbidité infantile. Comparés aux enfants nés à terme, les prématurés font face à des risques importants de troubles moteurs et cognitifs durant l'enfance, ainsi que de maladies chroniques et décès prématurés à l’âge adulte. La prématurité constitue un enjeu important de santé publique et en Europe, les taux varient entre 5 et 10%. Notre objectif pour cette thèse était de mieux comprendre les sources d’hétérogénéité des taux à l’échelle des pays. Dans un premier temps, nous avons effectué une revue exhaustive de la littérature qui montre que les caractéristiques maternelles, les pratiques médicales, et les méthodes d'estimation de l'âge gestationnel ont un impact sur les taux de prématurité. Cependant, ces facteurs n'expliquent pas l’ampleur des différences observées entre les pays. Puis, en utilisant des données sur les femmes enceintes, les nouveau-nés et les mort-nés dans 34 pays à revenus élevés de 1996 à 2010, nous avons établi que: 1) les différences d'enregistrement des naissances dans les pays à revenus élevés ont un impact limité sur les taux, sauf pour les naissances à 22-23 SA, 2) les tendances de PTB dans les pays sont associées à des variations plus importantes dans la distribution des âges gestationnels 3) et enfin, en utilisant les données d'un échantillon représentatif des naissances en France en 2010, qu’il existe des facteurs de risques maternels prénatals et socio-démographiques communs aux naissances avant terme (<37SA) et proche du terme à 37-38 SA. Viser à réduire les facteurs de risques de la naissance proche du terme et de la prématurité dans une approche conjointe pourrait apporter un nouvel élan à la prévention de la prématurité. Comparés aux enfants prématurés, les enfants nés proche du terme sont individuellement moins à risque, mais à l’échelle des pays ces enfants représentent environ une naissance sur quatre et ils contribuent de manière importante au fardeau de morbi-mortalité néonatale et infantile. Au niveau national, élargir les efforts de prévention de la prématurité à cette nouvelle population-cible pourrait avoir un plus grand impact sur la santé publique. / Preterm birth (PTB), defined as birth before 37 weeks, is a leading cause of infant mortality and morbidity. Compared to term infants, preterm infants face important risks of motor and cognitive impairments throughout childhood, as well as chronic diseases and premature death later in life. PTB represents a significant public health burden and in Europe, rates range between 5 and 10%. Such wide differences suggest that reductions may be possible, but there are few effective interventions, and these tend to target selected groups of high-risk pregnancies, based on clinical risk factors. Our aim for this thesis was to better appraise sources of population-level PTB rate variations and trends. First, we conducted an exhaustive review of the literature and found that maternal characteristics, reproductive policies, medical practices and methods of gestational age (GA) estimation affected PTB rates, but could not explain observed differences across countries. Next, using population-based data on pregnant women, newborns and stillbirths in 34 high-income countries from 1996 to 2010, we showed that: 1) reporting criteria for births and deaths affected PTB rates at early gestations and PTB rankings, but differences between countries with high and low rates are not just due to artefact 2) PTB trends were associated with broader shifts in countries’ gestational age GA distribution of births, and 3) using data from a representative sample of births in France in 2010, that there were shared maternal prenatal and socio-demographic risk factors for deliveries that did not reach full term, at 39 weeks GA. Our work confirms that recording differences in high-income countries have a limited impact on PTB rate variations. However, a broader focus on earlier delivery, including early term birth at 37-38 weeks, could shed light on the determinants of low PTB rates and provide a useful public health prevention paradigm.