- Email: [email protected]
Racial disparity in infant mortality
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Available online at www.sciencedirect.com
Seminars in Perinatology www.seminperinat.com
Racial disparity in infant mortality Nana Matoba, MD, MPH, and James W. Collins Jr, MD, MPH⁎ Division of Neonatology, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL
article info
abstra ct
Keywords:
In the United States, African-American infants have significantly higher mortality than
African-American
white infants. Previous work has identified associations between individual socioeconomic
preterm birth
factors and select community-level factors. In this review, the authors look beyond
infant mortality
traditional risk factors for infant mortality and examine the social context of race in this
racial disparity
country, in an effort to understand African-American women’s long-standing birth outcome disadvantage. In the process, recent insights are highlighted concerning neighborhood-level factors such as crime, segregation, built environment, and institutional racism, other likely causes for the poor outcomes of African-American infants in this country compared with infants in most other industrialized nations. & 2017 Published by Elsevier Inc.
Background Infant mortality rate (IMR) is more than a marker of maternal and child health; it is a symbolic benchmark of a society’s overall health. By this standard, the United States is deficient with the following 2 striking characteristics: its IMR is high compared with other developed nations, and African-American infants have a 2.2-fold greater mortality rate than white infants.1 Despite success in increased survival of preterm infants due to advances in obstetric and perinatal medicine over the last 3–4 decades, the U.S. ranking among industrialized countries has plummeted from 6th in the world to 26th in the past 50 years.2 During the same period, the African-American/ white infant mortality ratio has also increased from 1.6 to 2.2. Many observers suggest that these statistics are misleading because of international differences in the completeness of reporting of mortality, especially deaths at the threshold of viability, and variable birth registration requirements in other countries. However, even when births less than 22 weeks’ gestation are excluded, the preterm birth rate in the United States still exceeds that of Europe, and U.S. infant mortality rate remains greater than that of most European countries.3
In fact, the high preterm birth (o37 weeks' gestation, PTB) rate in the United States explains most of our nation’s low international standing in IMR. The percentage of PTB in the United States has risen more than 20% since 1990, and 36% since the early 1980s,4 and the United States compares favorably with Europe in the survival of infants born preterm (Fig. 1). Preterm infants have much higher rates of death or disability than infants born at 37 weeks of gestation or more, so the United States’ higher percentage of preterm births has a large impact on IMR. Disorders related to short gestation (o37 weeks) and low birth weight (o2500 g, LBW) are the leading cause of death for all African-American infants, whereas congenital malformations are the leading cause of death for white infants. The African-American/white mortality rate ratios range from 1.2 for congenital malformations to 3.5 for disorders of short gestation.1 Short gestation, or prematurity, is tightly linked with LBW and particularly with very low birth weight (VLBW; o1500 g). Importantly, LBW is a strong determinant of firstyear mortality and contributes to the racial disparity in IMR.1 Most pertinently, the approximately 1% of births occurring at a VLBW account for more than half of infant deaths and nearly
Grant support: Research Grant from the March of Dimes Foundation, United States (12_FY09_159 and 21_FY_16_111, J.W.C.). ⁎ Correspondence to: 225 E. Chicago Ave, Division of Neonatology, Box #45, Chicago IL, 60611. E-mail address: [email protected] (J.W. Collins). http://dx.doi.org/10.1053/j.semperi.2017.07.003 0146-0005/& 2017 Published by Elsevier Inc.
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VLBW rates (per 100)
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0.5 0 1950
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Fig. 1 – Seven decade trend in VLBW rates in the United States.
two-thirds of the racial gap in infant mortality.1 Among both African Americans and whites, the rates of VLBW has steadily increased in the last decades, but in 2013, African Americans had a VLBW rate of 2.8% compared to 1.1% for whites.4 Interestingly, the racial disparity persists among term infants. The leading causes of first-year mortality for African-American and white term infants are congenital malformations, sudden infant-death syndrome, and accidents (unintentional injuries).1 The mortality disadvantage of African-American term infants exists across all the major categories. Progress has been made in understanding the complicated issue of race, birth weight, and infant mortality, but challenges remain to identify and eliminate the effects of life-long underserved minority status on women’s health. The objective of this review is to look beyond traditional individual risk factors for infant mortality and examine the social context of race in this country, in an effort to understand AfricanAmerican women’s long-standing birth outcome disadvantage (Fig. 2). In the process, we highlight new approaches to capture the social determinants of the racial disparity in IMR.
Race and geographic ancestry Race has been viewed as a proxy for geographic ancestry, and some investigators have argued that disparities in birth outcomes result from genetic differences between African-American and white women because statistical adjustment for
Individual factors Perinatal factors
Race/ethnicity
Preterm Birth Low Birth Weight
Infant Mortality
Community factors
Fig. 2 – Conceptual framework for the relationship between individual and community factors, race/ethnicity, and infant mortality. (Adapted with permission from Lorch S, Enlow E. The role of social determinants in explaining racial/ethnic disparities in perinatal outcomes. Ped Res. 2016;79(1):141147.)
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socioeconomic factors did not fully eliminate racial disparities in infant mortality.5,6 However, this now seems implausible, since more than 90% of human genetic variation is found within the population of any continent, with only an additional 5–10% accounted for by differences in gene frequencies among continental populations.7,8 Rather than a traditional genetic concept, race should be viewed as a social construct. As such, social, economic, and cultural processes across the life-course are hypothesized to adversely impact historically disadvantaged populations in a multilayered manner.9–11 The investigation of immigrant women and their U.S.-born descendants strongly supports this conceptual model. Using Illinois vital records, we have found that the rates of LBW and VLBW among sub-Saharan African-born black women were less than that of U.S.-born black women and approximated that of U.S.-born white women.12 In a follow-up investigation, we reported that the birth weight of the U.S.-born female descendants of European-born white women increased across a generation.12 The opposite phenomenon occurred among the U.S.-born descendants of African/Caribbean-born black women, suggesting that an element closely related to life-long minority status is a risk factor for PTB.13 Similarly, Fang et al.14 have described births in New York City in which, within poor neighborhoods, immigrant black mothers had lower LBW rates than U.S.-born black mothers.
Traditional/individual factors Young maternal age, low education attainment, low income, unmarried marital status, short interpregnancy interval, health-eroding personal behaviors (cigarette smoking, alcohol intake, and illicit drug use), and inadequate prenatal care are well-documented risk factors for preterm birth and LBW.15–18 Yet, multiple studies have found that the racial disparity in the rates of PTB, LBW, and first-year mortality are independent of these traditional individual-level risk factors.15,19,20 The racial disparity in adverse birth outcome actually widens as women’s sociodemographic status, medical status, and behavioral status improves. Of particular note, college-graduated African-American (compared to white) women who receive adequate prenatal care still have more than a 2-fold greater LBW rate.21 Other speculated individual-level factors that contribute to racial disparity in infant mortality include prenatal care utilization,22 participation in prenatal Women, Infants, and Children (WIC) program,23 and paternal involvement in child-rearing.24 A limited literature shows that IMR of full-term AfricanAmerican infants exceeds that of whites.1 For term infants, congenital anomalies, SIDS, and injuries are the leading causes of death. Among congenital anomalies, congenital heart disease (CHD) is the leading cause of death. Using national vital records, a prior study recently found that term infants with U.S.-born African-American (compared to white) mothers had a 40% greater first-year mortality rate due to CHD independent of maternal age, education attainment, prenatal care usage, and region of residence. This disparity was widest during in the postneonatal (28–365 day) period, suggesting a neighborhood phenomenon.25
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Community/neighborhood effects The failure for individual-level characteristics to fully explain the racial disparities in birth outcomes has led to a surging interest in contextual factors, and in particular, residential neighborhood environments. Beyond individual factors, community factors are strongly associated with perinatal outcomes.26–30 Historically, African-American and white women have been exposed to extremes of residential environments with a disproportionately high percentage of African-American women exposed to urban poverty.27 Neighborhood poverty in adulthood is a well-established risk factor for adverse birth outcome independent of individual measures of socioeconomic status.31–33 Ahern et al.34 have found that, even when controlling for maternal cigarette smoking, neighborhood-level unemployment status was significantly associated with an increased risk of preterm delivery. In Canada, lower neighborhood socioeconomic status, measured by income level, was shown to adversely affect birth outcomes including preterm birth.35 Women living in the most deprived neighborhoods in Plymouth, England, were found to have increased risk of giving preterm birth, compared to the least deprived neighborhoods.36 For both white and African-American women, life-long residence in low-income neighborhoods is a risk factor for LBW, but African-American women experience a greater public health burden from this phenomenon. Across 2 generations, poverty exerts its effects strongly among African Americans: in Cook County, Illinois, rates of low birth weight rose as maternal grandmother’s residential environment during her pregnancy deteriorated, independently of mother’s residential environment during her pregnancy.37 In addition to neighborhood poverty, community-level factors such as racial residential segregation has received increased attention as a social determinant of racial disparities in birth outcomes. Thought to affect outcomes through neighborhood disadvantage (e.g., concentrated poverty, exposure to environmental stressors, and limited access to health services), racial segregation has been shown to be associated with decreased birth weight, increased rates of LBW, PTB, and infant mortality among African Americans.38–40 Using a spatial measure of neighborhood-level racial isolation of African Americans, Anthopolos et al.41 have shown that, infants born to African-American and white mothers living in African-American isolated neighborhoods had decreased birth weight and increased risk of low birth weight and preterm birth compared to counterparts in less isolated areas. In addition, white mothers in predominantly African-American neighborhoods experienced greater increases in odds of each poor birth outcomes than did African-American mothers, suggesting that black isolation is a proxy for concentrated socioeconomic disadvantage and access to positive features in the built environment.41 There is a growing interest on the effects of built environment on birth outcomes. Beyond residential segregation, measures such as housing damage, property damage, home vacancy, crime, and percentage of home rentals42 have been shown to affect risk of preterm birth. Features of the physical environment such as pollution and toxin exposure, and air
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quality, are beginning to be studied in their relation to birth outcomes. Recently, as seen in effects on adult health, exposure to urban residential greenness during pregnancy has been examined in association to birth weight, PTB, and SGA births.43 Using a satellite-derived index of vegetation within 100 m of mothers' homes in Canada, an interquartile increase in greenness index was associated with higher birth weight and decrease in SGA and PTB, adjusted for air pollution and noise exposures, neighborhood walkability, and park proximity. Similar studies of green space and birth outcomes have been documented in Spain44 and Portland, Oregon.45 The relationship of these built environment features to infant mortality is less well characterized to date, but in France, residential proximity to green space was examined in association to infant mortality.46 The authors found a clustered spatial distribution of infant mortality, which disappeared after adjustment for greenness and socioeconomic deprivation. Although these results suggest that greenness explains part of infant mortality, it is possible that, like residential segregation, green space is another proxy of socioeconomic status, and further research is required to validate these findings. Finally, violent crime is increasingly recognized as an element of the neighborhood environment not commonly investigated, and has been shown to be associated with low birthweight and preterm birth.47–49 In the city of Chicago in the 1980s, using Chicago Police Department violent crimes, the authors have shown that African-American mothers who resided in the most violent communities had a higher rate of SGA compared to mothers in the least violent communities.50 Since then, other studies have shown similar association between intrauterine growth restriction and violent crime,51 but measures of exposure (proximity vs area-level rate) remain variable defined, resulting in noncomparable associations across studies.47
Hypothesized mechanisms for racial disparity in infant mortality A life-course conceptual model has been proposed to explain the discordant pregnancy outcome and white and AfricanAmerican women in the United States.52 In this model, the racial disparity in U.S.-born women’s perinatal outcomes reflects a greater prevalence of prepregnancy risk factors and lower prevalence of protective factors among African Americans compared with whites. The hypothesized mechanisms include early-life (fetal) programming of reproductive potential and cumulative wear and tear (weathering). Researchers have used LBW as a proxy of aberrant female fetal reproductive programming. In both races, women who were themselves of LBW (compared to non-LBW) have greater rates of LBW, small-for-gestational-age (SGA) births, and preterm infants independent of traditional individual-level risk factors and neighborhood income.53,54,55 Interestingly, PTB rates fail to decrease among former LBW impoverishedborn African-American women who experience upward economic mobility during life-course.56 This suggests that mother’s in utero exposure to neighborhood poverty results in
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restricting fetal growth (as measured by LBW) and programs her reproductive physiology to deliver preterm infants during adulthood. Data from the Dutch Famine suggest that 2 successive generational exposure to nonimpoverishment is required to reverse the effects aberrant female fetal reproductive programming.57 The weathering hypothesis conceptualizes the physical consequences of social inequality on female reproductive outcome. Among white women, young and advanced maternal age are risk factors for LBW, but for African-American women, the risk for infant LBW grows with advancing age. This deterioration in reproductive health status over the childbearing years among African-American women has been described as “weathering,”58 or “accelerated aging” hypothesis, which state that (1) a decline in health status contributes to poorer reproductive outcomes as women age, and (2) social inequalities lead to an earlier and disproportionately greater decline in the health status of African Americans, resulting in a widening health differential with advancing age. There are multiple speculated pathways to weathering among African-American women, many of which constitute community contextual factors described above, such as delays in accessing health care, employment-related adverse health effects, more barriers to and fewer opportunities for a healthy lifestyle, exposure to air pollutants, high-risk behaviors, and excess stress caused by discrimination, violence, financial problems, housing insecurity, and lack of social support.59 Of note, such weathering phenomenon is conspicuously absent among white women. Even those living in poorer neighborhoods throughout lifetime do not show weathering with respect to LBW, SGA, or preterm birth,60 possibly reflecting a persistent inequality of exposure to the lowest income environments. Similarly, no group of white women, even cigarette smokers with an early-life or life-long residence in lower income neighborhoods exhibit weathering with regard to PTB.61,62 A weathering pattern of rising preterm birth rates with advancing age occurs only among African-American women with an early-life or life-long residence in lower income neighborhood.62 However, these studies defined lower income broadly, and may not have fully captured white women residing in disadvantaged areas. More detailed studies are needed to better delineate the agerelated patterns of PTB rates among white women with lifelong residence in lower income areas, which may reveal new findings with respect to their weathering.
Stress and exposure to racism Racial discrimination is a social context that African-American women must navigate throughout their lives. An expanding literature suggests that African-American women’s exposure to interpersonal racial discrimination is a risk factor for poor pregnancy outcomes. The underlying mechanism appears to be related to stress; physiologic responses to chronic exposure to stress can accumulate over time, leading to an enhanced inflammatory response, compromised fetal development, adverse pregnancy outcomes.63,64
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We previously found that African-American women who delivered preterm, LBW infants were more likely to experience interpersonal racial discrimination during their lifetime than African-American mothers who delivered term, nonLBW infants.65 The adverse effect of perceived discrimination was strongest among women aged 20–29 years, and generally considered as the optimal childbearing decade. This relationship between exposure to interpersonal racial discrimination and preterm birth appears to be modified by coping behaviors. A prior study reported that exposure to perceived interpersonal racism among African-American women in the past year was not associated with preterm birth in those mild/ moderate depressive symptoms, but was not associated with preterm birth in those with severe depressive symptoms, and those with or without high amounts of stress.66 The authors suggested that racism may not further impact a group already at high risk for preterm birth, but may increase the risk of preterm birth for women at lower baseline risk. Institutionalized racism permeates systems—education, health care, housing, justice, labor—and influences their health trajectory,67 and is gaining attention as another social determinant of birth outcomes. Mendez has recently studied the relationship between birth outcomes and institutional racism (structural racism, defined as differential access to resources and opportunities by race as well as policies, laws, and practices that reinforce racial inequity) in the form of residential redlining (neighborhood-level racial inequities in mortgage lending) across a diverse cohort of pregnant women.68 While African-American women were slightly more likely to live in redlined neighborhoods compared with all other racial/ethnic groups, there was no significant relationship between redlining and stress among the study population. Surprisingly, among African-American women, living in a redlined area was moderately associated with a decreased risk (aRR ¼ 0.8, 95% CI: 0.6, 0.99) of preterm birth.68 This was a surprising finding, perhaps explained by the fact that “residence in redlined areas may serve as a potentially protective factor for infant health due to neighborhood cohesion or social support, buffering experiences of stress and discrimination.”68,69 The authors also suggest that because the racial composition of redlined areas differed between homeowners and public/social renters, it is possible that redlining confers a differential association with preterm birth that varies by racial/ethnic group as a result of geographic sorting by race.68 Scholarly discussions of the role of racism in health disparities have led to awareness for the need for public health interventions to combat the environmental, economic, and cultural stressors specific to the African-American community’s experience. Community-based interventions to reduce African-American infant mortality are being attempted70 in local communities such as in Genesee County, Michigan, to address unrecognized and often unintentional prejudices by health care providers towards their patients. A community-based public health partnership, a coalition called Racial and Ethnic Approaches to Community Health Program (REACH) is aiming to address deep-rooted racial and ethnic stereotypes among health care providers by holding workshops and assessing their effectiveness in promoting an understanding of institutional racism and interpersonal
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racism pre- and post-assessment. These workshops attempt to look beyond a focus on the symptoms of racism, to an understanding of what it is, where it comes from, how it functions, why it persists, and how it can be undone. Facilitators (1 African American and 1 white) lecture on concepts and lead discussions with visual aids to mixed-race groups of 25–50 individuals from the health and educational sectors and community residents, emphasizing the history of slavery and racial discrimination as the genesis of current social inequalities. Undoubtedly, interventions to reduce racial health disparities in this country will take such innovative community-based efforts, in addition to ongoing clinical, scientific, and legislative efforts.
Summary and future research needs In the United States, African-American infants have significantly worse infant mortality than white infants. Individual risk factors alone do not explain this persistent gap, just as they did not explain the disparity in preterm birth and low birth weight. Recent studies in social determinants provide insight into the contribution of community and environmental factors to the racial disparity. Select community-level factors are potential, but partial, determinants of the racial disparity. Interpersonal and institutionalized racism is an important, and increasingly recognized, stressor for AfricanAmerican women with damaging consequences to maternal and child health. Eliminating racial disparity in infant mortality takes a lifecourse approach, addressing early life disadvantages, in addition to life-long exposure to social determinants ranging from neighborhood poverty, community factors such as crime, segregation, built environment, and racial discrimination.
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and pregnancy outcomes in a diverse, urban population. Soc Sci Med. 2007;65:2440–2457. Lu MC, Halfon N. Racial and ethnic disparities in birth outcomes: a life-course perspective. Matern Child Health J. 2003;7:13–30. Collins JW Jr., David RJ, Prachand NG, Pierce ML. Low birth weight across generations. Matern Child Health J. 2003;7:229–237. Simon DM, Vyas S, Prachand NG, David RJ, Collins JW Jr. Relation of maternal low birth weight to infant growth retardation and prematurity. Matern Child Health J. 2006;10: 321–327. McAndrew S, Chihara I, Rankin KM, Collins JW Jr. The relation of maternal birth weight to African-American and non-Latina white twin pregnancy outcomes: a population-based study. Matern Child Health J. 2016:531–539. Collins JW Jr., Rankin KM, David RJ. African American women’s lifetime upward economic mobility and preterm birth: the effect of fetal programming. Am J Public Health. 2011;101: 714–719. Veenendaal MV, Painter RC, de Rooij SR, et al. Transgenerational effects of prenatal exposure to the 1944-45 Dutch famine. BJOG. 2013;120:548–553. Geronimus AT. Black/white differences in the relationship of maternal age to birthweight: a population-based test of the weathering hypothesis. Soc Sci Med. 1996;42:589–597. Holzman C, Eyster J, Kleyn M, et al. Maternal weathering and risk of preterm delivery. Am J Public Health. 2009;99:1864–1871. Love C, David RJ, Rankin KM, Collins JW Jr. Exploring weathering: effects of lifelong economic environment and maternal age on low birth weight, small for gestational age, and preterm birth in African-American and white women. Am J Epidemiol. 2010;172:127–134. Collins JW, Rankin KM, Hedstrom AB. Exploring weathering: the relation of age to low birth weight among first generation and established United States-born Mexican-American women. Matern Child Health J. 2012;16:967–972. Hibbs S, Rankin KM, David RJ, Collins JW Jr. The relation of neighborhood income to the age-related patterns of preterm birth among white and African-American women: the effect of cigarette smoking. Matern Child Health J. 2016;20:1432–1440. Baum A, Garofalo JP, Yali AM. Socioeconomic status and chronic stress. Does stress account for SES effects on health? Ann N Y Acad Sci. 1999;896:131–144. Culhane JF, Rauh V, McCollum KF, Elo IT, Hogan V. Exposure to chronic stress and ethnic differences in rates of bacterial vaginosis among pregnant women. Am J Obstet Gynecol. 2002;187:1272–1276. Collins JW Jr., David RJ, Handler A, Wall S, Andes S. Very low birthweight in African American infants: the role of maternal exposure to interpersonal racial discrimination. Am J Public Health. 2004;94:2132–2138. Slaughter-Acey JC, Sealy-Jefferson S, Helmkamp L, et al. Racism in the form of micro aggressions and the risk of preterm birth among black women. Ann Epidemiol. 2016;26:7–13 e1. Willis E, McManus P, Magallanes N, Johnson S, Majnik A. Conquering racial disparities in perinatal outcomes. Clin Perinatol. 2014;41:847–875. Mendez DD, Hogan VK, Culhane JF. Institutional racism, neighborhood factors, stress, and preterm birth. Ethn Health. 2014;19:479–499. LaVeist TA. The political empowerment and health status of African Americans: mapping a new territory. Am J Sociol. 1992;97:1080–1095. Kruger DJ, Carty DC, Turbeville AR, French-Turner TM, Brownlee S. Undoing racism through Genesee County’s REACH infant mortality reduction initiative. Prog Community Health Partnersh. 2015;9:57–63.
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Available online at www.sciencedirect.com
Seminars in Perinatology www.seminperinat.com
Racial disparity in infant mortality Nana Matoba, MD, MPH, and James W. Collins Jr, MD, MPH⁎ Division of Neonatology, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL
article info
abstra ct
Keywords:
In the United States, African-American infants have significantly higher mortality than
African-American
white infants. Previous work has identified associations between individual socioeconomic
preterm birth
factors and select community-level factors. In this review, the authors look beyond
infant mortality
traditional risk factors for infant mortality and examine the social context of race in this
racial disparity
country, in an effort to understand African-American women’s long-standing birth outcome disadvantage. In the process, recent insights are highlighted concerning neighborhood-level factors such as crime, segregation, built environment, and institutional racism, other likely causes for the poor outcomes of African-American infants in this country compared with infants in most other industrialized nations. & 2017 Published by Elsevier Inc.
Background Infant mortality rate (IMR) is more than a marker of maternal and child health; it is a symbolic benchmark of a society’s overall health. By this standard, the United States is deficient with the following 2 striking characteristics: its IMR is high compared with other developed nations, and African-American infants have a 2.2-fold greater mortality rate than white infants.1 Despite success in increased survival of preterm infants due to advances in obstetric and perinatal medicine over the last 3–4 decades, the U.S. ranking among industrialized countries has plummeted from 6th in the world to 26th in the past 50 years.2 During the same period, the African-American/ white infant mortality ratio has also increased from 1.6 to 2.2. Many observers suggest that these statistics are misleading because of international differences in the completeness of reporting of mortality, especially deaths at the threshold of viability, and variable birth registration requirements in other countries. However, even when births less than 22 weeks’ gestation are excluded, the preterm birth rate in the United States still exceeds that of Europe, and U.S. infant mortality rate remains greater than that of most European countries.3
In fact, the high preterm birth (o37 weeks' gestation, PTB) rate in the United States explains most of our nation’s low international standing in IMR. The percentage of PTB in the United States has risen more than 20% since 1990, and 36% since the early 1980s,4 and the United States compares favorably with Europe in the survival of infants born preterm (Fig. 1). Preterm infants have much higher rates of death or disability than infants born at 37 weeks of gestation or more, so the United States’ higher percentage of preterm births has a large impact on IMR. Disorders related to short gestation (o37 weeks) and low birth weight (o2500 g, LBW) are the leading cause of death for all African-American infants, whereas congenital malformations are the leading cause of death for white infants. The African-American/white mortality rate ratios range from 1.2 for congenital malformations to 3.5 for disorders of short gestation.1 Short gestation, or prematurity, is tightly linked with LBW and particularly with very low birth weight (VLBW; o1500 g). Importantly, LBW is a strong determinant of firstyear mortality and contributes to the racial disparity in IMR.1 Most pertinently, the approximately 1% of births occurring at a VLBW account for more than half of infant deaths and nearly
Grant support: Research Grant from the March of Dimes Foundation, United States (12_FY09_159 and 21_FY_16_111, J.W.C.). ⁎ Correspondence to: 225 E. Chicago Ave, Division of Neonatology, Box #45, Chicago IL, 60611. E-mail address: [email protected] (J.W. Collins). http://dx.doi.org/10.1053/j.semperi.2017.07.003 0146-0005/& 2017 Published by Elsevier Inc.
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Fig. 1 – Seven decade trend in VLBW rates in the United States.
two-thirds of the racial gap in infant mortality.1 Among both African Americans and whites, the rates of VLBW has steadily increased in the last decades, but in 2013, African Americans had a VLBW rate of 2.8% compared to 1.1% for whites.4 Interestingly, the racial disparity persists among term infants. The leading causes of first-year mortality for African-American and white term infants are congenital malformations, sudden infant-death syndrome, and accidents (unintentional injuries).1 The mortality disadvantage of African-American term infants exists across all the major categories. Progress has been made in understanding the complicated issue of race, birth weight, and infant mortality, but challenges remain to identify and eliminate the effects of life-long underserved minority status on women’s health. The objective of this review is to look beyond traditional individual risk factors for infant mortality and examine the social context of race in this country, in an effort to understand AfricanAmerican women’s long-standing birth outcome disadvantage (Fig. 2). In the process, we highlight new approaches to capture the social determinants of the racial disparity in IMR.
Race and geographic ancestry Race has been viewed as a proxy for geographic ancestry, and some investigators have argued that disparities in birth outcomes result from genetic differences between African-American and white women because statistical adjustment for
Individual factors Perinatal factors
Race/ethnicity
Preterm Birth Low Birth Weight
Infant Mortality
Community factors
Fig. 2 – Conceptual framework for the relationship between individual and community factors, race/ethnicity, and infant mortality. (Adapted with permission from Lorch S, Enlow E. The role of social determinants in explaining racial/ethnic disparities in perinatal outcomes. Ped Res. 2016;79(1):141147.)
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socioeconomic factors did not fully eliminate racial disparities in infant mortality.5,6 However, this now seems implausible, since more than 90% of human genetic variation is found within the population of any continent, with only an additional 5–10% accounted for by differences in gene frequencies among continental populations.7,8 Rather than a traditional genetic concept, race should be viewed as a social construct. As such, social, economic, and cultural processes across the life-course are hypothesized to adversely impact historically disadvantaged populations in a multilayered manner.9–11 The investigation of immigrant women and their U.S.-born descendants strongly supports this conceptual model. Using Illinois vital records, we have found that the rates of LBW and VLBW among sub-Saharan African-born black women were less than that of U.S.-born black women and approximated that of U.S.-born white women.12 In a follow-up investigation, we reported that the birth weight of the U.S.-born female descendants of European-born white women increased across a generation.12 The opposite phenomenon occurred among the U.S.-born descendants of African/Caribbean-born black women, suggesting that an element closely related to life-long minority status is a risk factor for PTB.13 Similarly, Fang et al.14 have described births in New York City in which, within poor neighborhoods, immigrant black mothers had lower LBW rates than U.S.-born black mothers.
Traditional/individual factors Young maternal age, low education attainment, low income, unmarried marital status, short interpregnancy interval, health-eroding personal behaviors (cigarette smoking, alcohol intake, and illicit drug use), and inadequate prenatal care are well-documented risk factors for preterm birth and LBW.15–18 Yet, multiple studies have found that the racial disparity in the rates of PTB, LBW, and first-year mortality are independent of these traditional individual-level risk factors.15,19,20 The racial disparity in adverse birth outcome actually widens as women’s sociodemographic status, medical status, and behavioral status improves. Of particular note, college-graduated African-American (compared to white) women who receive adequate prenatal care still have more than a 2-fold greater LBW rate.21 Other speculated individual-level factors that contribute to racial disparity in infant mortality include prenatal care utilization,22 participation in prenatal Women, Infants, and Children (WIC) program,23 and paternal involvement in child-rearing.24 A limited literature shows that IMR of full-term AfricanAmerican infants exceeds that of whites.1 For term infants, congenital anomalies, SIDS, and injuries are the leading causes of death. Among congenital anomalies, congenital heart disease (CHD) is the leading cause of death. Using national vital records, a prior study recently found that term infants with U.S.-born African-American (compared to white) mothers had a 40% greater first-year mortality rate due to CHD independent of maternal age, education attainment, prenatal care usage, and region of residence. This disparity was widest during in the postneonatal (28–365 day) period, suggesting a neighborhood phenomenon.25
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Community/neighborhood effects The failure for individual-level characteristics to fully explain the racial disparities in birth outcomes has led to a surging interest in contextual factors, and in particular, residential neighborhood environments. Beyond individual factors, community factors are strongly associated with perinatal outcomes.26–30 Historically, African-American and white women have been exposed to extremes of residential environments with a disproportionately high percentage of African-American women exposed to urban poverty.27 Neighborhood poverty in adulthood is a well-established risk factor for adverse birth outcome independent of individual measures of socioeconomic status.31–33 Ahern et al.34 have found that, even when controlling for maternal cigarette smoking, neighborhood-level unemployment status was significantly associated with an increased risk of preterm delivery. In Canada, lower neighborhood socioeconomic status, measured by income level, was shown to adversely affect birth outcomes including preterm birth.35 Women living in the most deprived neighborhoods in Plymouth, England, were found to have increased risk of giving preterm birth, compared to the least deprived neighborhoods.36 For both white and African-American women, life-long residence in low-income neighborhoods is a risk factor for LBW, but African-American women experience a greater public health burden from this phenomenon. Across 2 generations, poverty exerts its effects strongly among African Americans: in Cook County, Illinois, rates of low birth weight rose as maternal grandmother’s residential environment during her pregnancy deteriorated, independently of mother’s residential environment during her pregnancy.37 In addition to neighborhood poverty, community-level factors such as racial residential segregation has received increased attention as a social determinant of racial disparities in birth outcomes. Thought to affect outcomes through neighborhood disadvantage (e.g., concentrated poverty, exposure to environmental stressors, and limited access to health services), racial segregation has been shown to be associated with decreased birth weight, increased rates of LBW, PTB, and infant mortality among African Americans.38–40 Using a spatial measure of neighborhood-level racial isolation of African Americans, Anthopolos et al.41 have shown that, infants born to African-American and white mothers living in African-American isolated neighborhoods had decreased birth weight and increased risk of low birth weight and preterm birth compared to counterparts in less isolated areas. In addition, white mothers in predominantly African-American neighborhoods experienced greater increases in odds of each poor birth outcomes than did African-American mothers, suggesting that black isolation is a proxy for concentrated socioeconomic disadvantage and access to positive features in the built environment.41 There is a growing interest on the effects of built environment on birth outcomes. Beyond residential segregation, measures such as housing damage, property damage, home vacancy, crime, and percentage of home rentals42 have been shown to affect risk of preterm birth. Features of the physical environment such as pollution and toxin exposure, and air
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quality, are beginning to be studied in their relation to birth outcomes. Recently, as seen in effects on adult health, exposure to urban residential greenness during pregnancy has been examined in association to birth weight, PTB, and SGA births.43 Using a satellite-derived index of vegetation within 100 m of mothers' homes in Canada, an interquartile increase in greenness index was associated with higher birth weight and decrease in SGA and PTB, adjusted for air pollution and noise exposures, neighborhood walkability, and park proximity. Similar studies of green space and birth outcomes have been documented in Spain44 and Portland, Oregon.45 The relationship of these built environment features to infant mortality is less well characterized to date, but in France, residential proximity to green space was examined in association to infant mortality.46 The authors found a clustered spatial distribution of infant mortality, which disappeared after adjustment for greenness and socioeconomic deprivation. Although these results suggest that greenness explains part of infant mortality, it is possible that, like residential segregation, green space is another proxy of socioeconomic status, and further research is required to validate these findings. Finally, violent crime is increasingly recognized as an element of the neighborhood environment not commonly investigated, and has been shown to be associated with low birthweight and preterm birth.47–49 In the city of Chicago in the 1980s, using Chicago Police Department violent crimes, the authors have shown that African-American mothers who resided in the most violent communities had a higher rate of SGA compared to mothers in the least violent communities.50 Since then, other studies have shown similar association between intrauterine growth restriction and violent crime,51 but measures of exposure (proximity vs area-level rate) remain variable defined, resulting in noncomparable associations across studies.47
Hypothesized mechanisms for racial disparity in infant mortality A life-course conceptual model has been proposed to explain the discordant pregnancy outcome and white and AfricanAmerican women in the United States.52 In this model, the racial disparity in U.S.-born women’s perinatal outcomes reflects a greater prevalence of prepregnancy risk factors and lower prevalence of protective factors among African Americans compared with whites. The hypothesized mechanisms include early-life (fetal) programming of reproductive potential and cumulative wear and tear (weathering). Researchers have used LBW as a proxy of aberrant female fetal reproductive programming. In both races, women who were themselves of LBW (compared to non-LBW) have greater rates of LBW, small-for-gestational-age (SGA) births, and preterm infants independent of traditional individual-level risk factors and neighborhood income.53,54,55 Interestingly, PTB rates fail to decrease among former LBW impoverishedborn African-American women who experience upward economic mobility during life-course.56 This suggests that mother’s in utero exposure to neighborhood poverty results in
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restricting fetal growth (as measured by LBW) and programs her reproductive physiology to deliver preterm infants during adulthood. Data from the Dutch Famine suggest that 2 successive generational exposure to nonimpoverishment is required to reverse the effects aberrant female fetal reproductive programming.57 The weathering hypothesis conceptualizes the physical consequences of social inequality on female reproductive outcome. Among white women, young and advanced maternal age are risk factors for LBW, but for African-American women, the risk for infant LBW grows with advancing age. This deterioration in reproductive health status over the childbearing years among African-American women has been described as “weathering,”58 or “accelerated aging” hypothesis, which state that (1) a decline in health status contributes to poorer reproductive outcomes as women age, and (2) social inequalities lead to an earlier and disproportionately greater decline in the health status of African Americans, resulting in a widening health differential with advancing age. There are multiple speculated pathways to weathering among African-American women, many of which constitute community contextual factors described above, such as delays in accessing health care, employment-related adverse health effects, more barriers to and fewer opportunities for a healthy lifestyle, exposure to air pollutants, high-risk behaviors, and excess stress caused by discrimination, violence, financial problems, housing insecurity, and lack of social support.59 Of note, such weathering phenomenon is conspicuously absent among white women. Even those living in poorer neighborhoods throughout lifetime do not show weathering with respect to LBW, SGA, or preterm birth,60 possibly reflecting a persistent inequality of exposure to the lowest income environments. Similarly, no group of white women, even cigarette smokers with an early-life or life-long residence in lower income neighborhoods exhibit weathering with regard to PTB.61,62 A weathering pattern of rising preterm birth rates with advancing age occurs only among African-American women with an early-life or life-long residence in lower income neighborhood.62 However, these studies defined lower income broadly, and may not have fully captured white women residing in disadvantaged areas. More detailed studies are needed to better delineate the agerelated patterns of PTB rates among white women with lifelong residence in lower income areas, which may reveal new findings with respect to their weathering.
Stress and exposure to racism Racial discrimination is a social context that African-American women must navigate throughout their lives. An expanding literature suggests that African-American women’s exposure to interpersonal racial discrimination is a risk factor for poor pregnancy outcomes. The underlying mechanism appears to be related to stress; physiologic responses to chronic exposure to stress can accumulate over time, leading to an enhanced inflammatory response, compromised fetal development, adverse pregnancy outcomes.63,64
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We previously found that African-American women who delivered preterm, LBW infants were more likely to experience interpersonal racial discrimination during their lifetime than African-American mothers who delivered term, nonLBW infants.65 The adverse effect of perceived discrimination was strongest among women aged 20–29 years, and generally considered as the optimal childbearing decade. This relationship between exposure to interpersonal racial discrimination and preterm birth appears to be modified by coping behaviors. A prior study reported that exposure to perceived interpersonal racism among African-American women in the past year was not associated with preterm birth in those mild/ moderate depressive symptoms, but was not associated with preterm birth in those with severe depressive symptoms, and those with or without high amounts of stress.66 The authors suggested that racism may not further impact a group already at high risk for preterm birth, but may increase the risk of preterm birth for women at lower baseline risk. Institutionalized racism permeates systems—education, health care, housing, justice, labor—and influences their health trajectory,67 and is gaining attention as another social determinant of birth outcomes. Mendez has recently studied the relationship between birth outcomes and institutional racism (structural racism, defined as differential access to resources and opportunities by race as well as policies, laws, and practices that reinforce racial inequity) in the form of residential redlining (neighborhood-level racial inequities in mortgage lending) across a diverse cohort of pregnant women.68 While African-American women were slightly more likely to live in redlined neighborhoods compared with all other racial/ethnic groups, there was no significant relationship between redlining and stress among the study population. Surprisingly, among African-American women, living in a redlined area was moderately associated with a decreased risk (aRR ¼ 0.8, 95% CI: 0.6, 0.99) of preterm birth.68 This was a surprising finding, perhaps explained by the fact that “residence in redlined areas may serve as a potentially protective factor for infant health due to neighborhood cohesion or social support, buffering experiences of stress and discrimination.”68,69 The authors also suggest that because the racial composition of redlined areas differed between homeowners and public/social renters, it is possible that redlining confers a differential association with preterm birth that varies by racial/ethnic group as a result of geographic sorting by race.68 Scholarly discussions of the role of racism in health disparities have led to awareness for the need for public health interventions to combat the environmental, economic, and cultural stressors specific to the African-American community’s experience. Community-based interventions to reduce African-American infant mortality are being attempted70 in local communities such as in Genesee County, Michigan, to address unrecognized and often unintentional prejudices by health care providers towards their patients. A community-based public health partnership, a coalition called Racial and Ethnic Approaches to Community Health Program (REACH) is aiming to address deep-rooted racial and ethnic stereotypes among health care providers by holding workshops and assessing their effectiveness in promoting an understanding of institutional racism and interpersonal
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racism pre- and post-assessment. These workshops attempt to look beyond a focus on the symptoms of racism, to an understanding of what it is, where it comes from, how it functions, why it persists, and how it can be undone. Facilitators (1 African American and 1 white) lecture on concepts and lead discussions with visual aids to mixed-race groups of 25–50 individuals from the health and educational sectors and community residents, emphasizing the history of slavery and racial discrimination as the genesis of current social inequalities. Undoubtedly, interventions to reduce racial health disparities in this country will take such innovative community-based efforts, in addition to ongoing clinical, scientific, and legislative efforts.
Summary and future research needs In the United States, African-American infants have significantly worse infant mortality than white infants. Individual risk factors alone do not explain this persistent gap, just as they did not explain the disparity in preterm birth and low birth weight. Recent studies in social determinants provide insight into the contribution of community and environmental factors to the racial disparity. Select community-level factors are potential, but partial, determinants of the racial disparity. Interpersonal and institutionalized racism is an important, and increasingly recognized, stressor for AfricanAmerican women with damaging consequences to maternal and child health. Eliminating racial disparity in infant mortality takes a lifecourse approach, addressing early life disadvantages, in addition to life-long exposure to social determinants ranging from neighborhood poverty, community factors such as crime, segregation, built environment, and racial discrimination.
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