The Epidemiology of Preterm Birth and Neonatal Death Following Preterm Birth among Pacific Islanders
Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Public Health
First Advisor
Hawley, Nicola
Abstract
Background: Compared to other developed countries, the US has among the poorest maternal and child health outcomes. In the past five years, even though the neonatal mortality rate in the US decreased, the prevalence of preterm birth, the leading cause of neonatal death, increased. Racial disparities are evident in maternal and child health outcomes in the US, with Black women and infants having poor outcomes compared to White. Pacific Islanders are one of the fastest-growing minority populations in the US, yet they have been underrepresented in perinatal health research – either omitted due to small sample size or aggregated with Asian Americans. In other global settings, there are also millions of Pacific Islanders residing in New Zealand, Australia, and over ~1,000 islands across 300,000 square miles of the Pacific Ocean. Limited studies have, however, reported perinatal outcomes of Pacific Islanders in these contexts. Since Pacific Islanders have a relatively higher prevalence of obesity compared to other populations, it may be expected (based on literature from other populations) that Pacific Islanders would have a higher risk of both preterm birth and neonatal death. Therefore, the objective of this dissertation was to understand the epidemiology of preterm birth and neonatal death following preterm birth among Pacific Islanders. Methods: This dissertation includes five papers. For the first study (Chapter 2), we performed a systematic review and meta-analysis to estimate preterm birth prevalence in different global settings using prevalence meta-analyses and explored whether racial disparities were evident in preterm birth among Pacific Islanders compared to White/European women using Bayesian meta-analyses. In the second study (Chapter 3), we narrowed our focus to the US and US-affiliated Pacific Islands and conducted a systematic review and meta-analysis of literature published after 2010 to estimate preterm birth prevalence among Pacific Islanders, to examine whether Pacific Islanders had a higher risk of preterm birth compared to White women, and to summarize the most commonly identified risk factors associated with preterm birth among this population. In the following chapters, we used birth cohort data linked to birth-infant death data files from the US National Center for Health Statistics. For the third study (Chapter 4), we estimated the association between the rate of gestational weight gain and preterm birth, and how this association was modified by pre-pregnancy body mass index. For the fourth study (Chapter 5), we used both conventional birth-based and fetuses-at-risk approaches to identify risk factors associated with neonatal death following preterm birth among Pacific Islanders. In the fifth study (Chapter 6), we generated a graphical neonatal survival prediction tool using neonatal sex, gestational age, and birth weight. Results: We found that Pacific Islanders in the US had a higher prevalence of preterm birth compared to other global settings, although limited data from other global settings should be noted. Pacific Islanders resident in the US had a higher risk of preterm birth than White women in the US, yet the risk in New Zealand was similar between Pacific Islander and European women (Chapter 2); likely a result of more supportive health policies in the New Zealand setting. In literature from the US and the US-Affiliated Pacific Islands, Marshallese women were identified having an approximately twice the prevalence of preterm birth compared to Pacific Islander mothers of other ethnicities. Meanwhile, four risk factors for preterm birth could be explored with the data available: hypertension, diabetes, smoking, and pre-pregnancy body mass index. Hypertension and diabetes significantly increased the odds of preterm birth; however, no association was observed between pre-pregnancy body mass index and preterm birth (Chapter 3). We further explored the association among pre-pregnancy body mass index, rate of gestational weight gain, and preterm birth (Chapter 4). We found that the association between rate of gestational weight gain below or above the Institute of Medicine guidelines with preterm birth differed by pre-pregnancy body mass index among Pacific Islanders. We did not, however, observe an association between rate of gestational weight gain and preterm birth among mothers with the most severe obesity (Class III) before pregnancy. This finding leads to methodological questions about whether more fetal death occurred among mothers with extreme obesity pre-pregnancy, excluding them from our live birth data and potentially biasing findings among this group. There are similar concerns about how conventional birth-based approaches used in studies exploring neonatal outcomes following preterm birth may be vulnerable to bias due to overadjustment with stratification. Therefore, in the next chapter, risk factors for preterm birth were examined using both birth-based and fetuses-at-risk approaches. As well as eight risk factors identified in the birth-based approach, five additional influencing factors were identified by the fetuses-at-risk approach. Both birth-based and fetuses-at-risk approaches have pros and cons, so combining results from these two approaches would more comprehensively inform interventions to prevent neonatal death among Pacific Islanders born preterm (Chapter 5). Finally, using neonatal sex, gestational age, and birth weight we created a graphical tool to predict neonatal survival among Pacific Islander singletons in the US (Chapter 6). Conclusions: This dissertation addressed several gaps in the literature describing perinatal outcomes among Pacific Islanders in the US, and highlighted the remaining knowledge gaps present in other global settings. Lack of data remains a major obstacle to a better understanding of the epidemiology of preterm birth among this population, but these studies highlight an overall increased risk of both preterm birth and neonatal death among Pacific Islanders. While the original questions addressed in this thesis were motivated by the high levels of overweight and obesity among Pacific Islanders, the findings generated new questions about our ability to understand risk in the most extreme obesity classes given potential biases in our methodological approach. A recurring theme throughout this thesis is how methodological design is important in perinatal research to avoid potential over-adjustment, stratification bias, or selection bias. Future research should continue to disaggregate Pacific Islanders from Asian Americans or other races in different settings to address the current sparsity of Pacific Islander focused studies in epidemiologic data. We also recommend future studies for neonatal mortality or morbidity following preterm birth using both birth-based and fetuses-at-risk approaches to provide a clearer picture between prenatal characteristics and neonatal outcomes, since gestational age is in the causal pathway of those associations and may modify the outcomes. Importantly, in expanding our understanding of preterm birth and neonatal death following preterm birth among Pacific Islanders this thesis highlights the need for future interventions to decrease adverse perinatal health outcomes in this population.
Recommended Citation
Wu, Bohao, "The Epidemiology of Preterm Birth and Neonatal Death Following Preterm Birth among Pacific Islanders" (2023). Yale Graduate School of Arts and Sciences Dissertations. 919.
https://elischolar.library.yale.edu/gsas_dissertations/919
