Pre-term infant births, and the disparities associated with the condition, remain an extremely salient issue despite substantial improvements across many domains of neonatal healthcare in the past two decades. The World Health Organization defines pre-term birth as the delivery of infants before the full term – 37 weeks of pregnancy – has been completed (World Health Organization, 2010). Preterm birth complications continue to be the leading cause of death among children under 5 years of age, and in 2015 alone, preterm birth was cited as the cause of death for approximately 1 million infants. Furthermore, infants who do survive early preterm delivery are often faced with lifelong morbidity, including physiological and neurodevelopmental disabilities, and the costs associated with medical care for prematurely delivered infants is debilitating for many families. Despite improvements in rates of mortality across other domains in NICU’s around the United States, each year an estimated 15 million babies are born preterm, and this number is continuing to rise (Liu et al., 2016). It is estimated that nearly one in every eight infants in the United States is born early (Frey & Klebanoff, 2016). These rising rates however, are not consistent across all demographics, and disparities among preterm birth incidence and survival rates of prematurely delivered newborns are stark. Multiple etiologic pathways, including social, environmental and geographical, as well as biological factors all play a role in the differences in observed sociodemographic, behavioral, and medical risk factors and rates of incidence, and are important to consider when addressing the disparities associated with the access to preventative care, incidence of, and outcomes associated with premature delivery.
One of the most significant, persistent and widely publicized health disparities associated with preterm births is the racial and ethnic disparity in the rates of premature delivery in the United States. Research indicates babies born to Black mothers in the United States are two times more likely to be born prematurely than infants born to white mothers (Carmichael et al., 2017). In 2015, 13.4% of births to Black mothers in the United States were preterm, compared to 9.1% among Latina and 8.9% among non-Hispanic Whites (Pearl et al., 2018). The driving forces behind this racial disparity are not well understood, and many researchers have attempted to flush out the multitude of factors that contribute to such a shocking statistic. Most available work has focused on socioeconomic status, including income, wealth and education at the individual and household level as a driving force behind the differences in rates of preterm birth (PTB). A review of studies examining relationships between socioeconomic status and adverse birth outcomes found that 93 out of 106 studies reported a significant association between a socioeconomic measure and a birth outcomes (Braveman et al. 2015), however many with varying and sometimes inconsistent results when considering subgroups. Among highly disadvantaged women (lowest SES), many studies have found little to no Black-White disparities in incidence of preterm birth. Other studies have identified significant racial disparity among socioeconomically disadvantaged women, but have identified even greater racial disparities among high SES women. These inconsistencies in findings reflect the complex nature of the disparity and the challenges associated with ascribing one factor as the primary cause behind a health inequality. These inconsistencies suggest socioeconomic status play a moderator role, but necessitate the investigation of other specific factors, including biological, social, and greater environmental factors that might also be associated with the Black-white disparity in PTB, and that might serve as more effectual points for intervention when attempting to combat the disparity.
While the role of socioeconomic factors in the Black-white PTB disparity in the United States is undoubtedly important, in order to create the most effective interventions, it is necessary to consider other specific, quantifiable factors that likely also play a role, while perhaps acting the ambiguous umbrella term of SES. A number of recent studies suggest that gestational weight is significantly associated with rates of preterm birth and may act as a modifiable contributor to the Black-white disparity in PTB (Leonard et al., 2016). It is well documented that higher rates of preterm birth occur in women who are underweight or obese prior to pregnancy, as well as in women who fail meet appropriate weight gain during pregnancy. Research indicates non-Hispanic Black women, compared to white women, are more likely to begin pregnancy obese, thus putting Black women at an increased risk of premature delivery. Furthermore, non-Hispanic Black women who enter pregnancy either underweight or at normal weight are less likely to meet recommended gestational weight gains compared with non-Hispanic white women, again conferring increased risk of PTB (Leonard et al., 2016). Poor nutrition and consequently, obesity or failure to meet weight gain is inextricably linked with socioeconomic status, given that lower SES populations have decreased access to food (and specifically healthy food) resources, and medical resources that might advise expecting mothers on how to meet proper gestational weight goals. Thus, disparities in weight gain, or lack thereof during pregnancy, is likely an underlying factor that moderates, in part, the PTB Black-white disparity.
Just as obesity and low gestational weight are recognized as immediate causes of preterm delivery, chronic stress and anxiety in expecting mothers has been widely documented as a precipitating factor for preterm birth (Staneva, Bogossian, Pritchard & Wittkowski, 2015). McEwen & McEwen’s model of toxic stress and allostatic overload highlights the neuro and physiological consequences of chronic stress and adversity, including dysregulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis, which is responsible for regulating levels of cortisol levels, metabolic hormones and components of the immune system (McEwen & McEwen, 2017). Consequently, chronic stress (and the frequently comorbid anxiety and depression) during pregnancy induces physiologic changes, including elevated cortisol releasing hormone (CRH), which in turn leads to increases in levels of prostaglandins and inflammatory cytokines, both of which are associated with uterine contractions and spontaneous preterm birth (Wheeler et al., 2018). Furthermore, acute psychosocial stress has also been linked to increased risk of contracting bacterial vaginosis – a common bacterial infection that is considered as a risk factor for preterm birth, and that is more prevalent in Black than white women (Kramer & Hogue, 2009). Likely as the result of the psychosocial consequences of racism and discrimination across in the lifespan, non-Hispanic Black women, regardless of income level, are most likely to experience such chronic stress pre-conception as well as during pregnancy (Grobman et al., 2016). Thus, a contributor to the Black-white disparities in obstetric outcomes is differences in stress experienced by non-Hispanic Black women.
While discrimination and the resulting chronic stress across the lifespan can directly lead to serious physiological consequences during gestation, Stereotype threat may also act as an overlooked social barrier that functions to increase the risk of PTB for non-Hispanic Black women. Joshua Aronson’s model of Stereotype threat – “a disruptive psychological state that people experience when they feel at risk for confirming a negative stereotype associated with their social identity” – in the healthcare setting highlights how unconscious bias can affect quality of healthcare and healthcare outcomes (Aronson et al., 2013). Research indicates that stereotypical perceptions of Black women are highly prevalent within the medical community, and that physicians feel less affiliation with Black patients compared with White patients (Abdou & Fingerhut, 2014). In turn, non-Hispanic Black (NHB) women feel stress of anticipated and actual experiences of biased treatment and report significantly greater anxiety and worry in healthcare settings than their white counterparts. These findings have serious implications. A lack of patient-provider trust, effective communication, and comfort is likely to decrease the quality of medical care that the patient will receive and decreases the likelihood of the patient’s adherence to health behaviors (Abdou & Fingerhut, 2014). Research suggests the affective outcomes of these negative patient-provider interactions, in combination with the physiological stress as a result of stereotype threat, may put pregnant Black women at a significantly greater risk for obstetric complications such as preterm birth (Wheeler et al., 2018).
Beyond the social and biological mechanisms that may underlie the Black-white disparity in preterm deliveries, ambient environmental factors also play a role. Research has been directed towards investigating the relationship of PTB with modifiable aspects of the environment in an effort to identify points for effective intervention to reduce the disparity. Ongoing research in California suggests that air pollution, specifically neighborhood air pollution, is linked with preterm birth. Residential segregation patterns and the high proportion of Black women living in urban, low SES, and highly polluted areas serve to explain in part the alarming results of the study and analysis. Researchers at the University of California found “differences in mean annual PM2:5 [particulate matter pollutant] to explain nearly as much of the PTB [Black-White] disparity as recognized strong predictors of PTB, such as maternal age and education” (Benmarhnia et al., 2017). These findings further support the idea that the Black-white disparity in preterm delivery can be explained not just by socioeconomic status, but by several significant predictors including individual demographics, neighborhood socioeconomic environment, and neighborhood air pollution that act in conjunction.
Currently, the best intervention methods to target the Black-white preterm birth disparity remain unclear – few interventions have been designed to specifically address the increased preterm birth rates in non-Hispanic Black women, and interventions aimed at reducing general rates of preterm birth have been demonstrated largely ineffective, and a small portion have even been found to be harmful (Piso et al., 2014; Stock & Ismail, 2016). The American Public Health Association’s statement regarding policy to address preterm birth disparities essentially states that reexamination of the explanatory models of the disparity must occur before any interventions can be attempted or changes in policy can occur, as current models remain unable to account for the persistent disparities in PTB. The APHA posits “Educating the public and health care providers, broadening access to quality health care services, promoting healthier physical and social environments, supporting innovative research, and advocating for efforts to address racial and social inequalities can be effective tools in reducing disparities in preterm births and low birthweight.”
Targeting socioeconomic inequality in an effort to combat the health disparities associated with preterm birth would be, at the moment, a cost and time ineffective and largely futile method to directly address PTB rates. Therefore, it is important to design policy and targeted interventions that address other more easily defined and malleable risk factors for preterm birth, beyond socioeconomic status. The adverse health effects of chronic stress associated with Aronson’s Stereotype bias and the implications of negative patient-provider interactions as a result of stereotype bias highlight a point where effective intervention might be possible. Campaigns to educate physicians on the existence of this subconscious stereotype bias and providing the physicians with the tools to actively work against it – such as improved methods for communicating and establishing trusting relationships with patients subject to this bias – would be an easy and relatively cost free method of beginning to address the Black-white disparity in preterm births. By establishing more trusting relationships with the cohort at risk, not only would this likely increase the quality of care that the patient (and subsequently her unborn child) would receive, but it would likely increase the probability that the patient would adhere to physician-directed health behaviors, and it would begin to alleviate (however small) a portion of the chronic psychosocial stress felt by Black women as a result of stereotype threat and improve their overall health – thereby decreasing the likelihood of the occurrence of preterm birth. Given the research on the importance of appropriate weight gain during pregnancy in preventing preterm birth, another manner to address the disparity would be to create resource centers, which dually function as food banks, in low SES, highly demographically Black areas, exclusively for expecting mothers. These resource centers would provide nutritional counseling for overweight expecting mothers, and act as a food bank where severely underweight pregnant women could receive food. Most importantly, these resource centers would act to educate the surrounding community and disseminate information regarding the dangers of inappropriate gestational weight gain and the serious risks associated with preterm delivery. While ensuring that each patient receives proper nutrition, especially in low income and food insecure areas, is not wholly achievable, patient accessibility to even just a few resource centers could serve to make a difference. Finally, to combat the risk factor of PM2:5 air pollution for preterm birth, policy might be implemented to effectively limit the amount of ambient PM2:5 especially in urban neighborhoods, and enforce routine testing to ensure that levels stay within a range deemed safe for human and fetal exposure. Furthermore, federal tax-breaks could be offered to factories who kept PM2:5 emittance levels below a certain threshold in urban, dense areas that are largely demographically Black, and where the ambient pollution levels were already high.
The biggest challenge in addressing the Black-white disparity associated with preterm births is that it’s causes are still not fully understood. As Link and Phelan’s theory of the fundamental causes of health inequalities suggests, socioeconomic status and social conditions act as fundamental causes of disease and mortality (Link & Phelan, 1995). This holds true however, because socioeconomic status embodies a range of resources that act in concert to either confer disadvantage or advantage with regards to rates of morbidity and mortality. Therefore, when considering the fundamental causes of the Black-white health disparity associated with preterm birth, it is impossible and unproductive to ascribe SES as a single driving force. Rather, socioeconomic status should be viewed as a modulator of a collection of risk or protective factors, which can then be specifically addressed in targeted interventions. Social structure, including latent institutionalized and interpersonal racism confer risk factors for non-Hispanic Black women in terms of economic disparities and deleterious environmental exposures based on demographics, which can act as distal causes of disease, while interpersonal racism in the healthcare setting combined with biological mechanisms act as more proximal causes of disease and preterm birth. In understanding the synthesis of the biological, social, and environmental determinants of health and by creating more complex models that outline the account for the equifinality of disease such as preterm birth, it will be possible to design significantly more effective, immediate interventions, potentially alleviate the current disparities regarding race and preterm birth, and most importantly, save lives.