Sharon E. Edwards

Environmental Contributions to Disparities in Pregnancy Outcomes

One of the most persistent disparities in American health status is the pronounced difference in birth outcomes between non-Hispanic black and non-Hispanic white women. Poor pregnancy outcomes have a substantial impact on mortality, morbidity, and health care costs. Increasing evidence indicates that environmental exposures are associated with poor birth outcomes. This paper reviews the latest research on how environmental exposures affect pregnancy outcomes and then discusses how these exposures may be embedded within a context of significant social and host factor stress. The analysis suggests that environmental, social, and host factors are cumulatively stressing non-Hispanic black women and that this cumulative stress may be a cause of the persistent disparities in pregnancy outcomes.

Making the environmental justice grade: the relative burden of air pollution exposure in the United States

This paper assesses whether the Clean Air Act and its Amendments have been equally successful in ensuring the right to healthful air quality in both advantaged and disadvantaged communities in the United States. Using a method to rank air quality established by the American Lung Association in its 2009 State of the Air report along with EPA air quality data, we assess the environmental justice dimensions of air pollution exposure and access to air quality information in the United States. We focus on the race, age, and poverty demographics of communities with differing levels of ozone and particulate matter exposure, as well as communities with and without air quality information. Focusing on PM2.5 and ozone, we find that within areas covered by the monitoring networks, non-Hispanic blacks are consistently overrepresented in communities with the poorest air quality. The results for older and younger age as well as poverty vary by the pollution metric under consideration. Rural areas are typically outside the bounds of air quality monitoring networks leaving large segments of the population without information about their ambient air quality. These results suggest that substantial areas of the United States lack monitoring data, and among areas where monitoring data are available, low income and minority communities tend to experience higher ambient pollution levels.

The effects of exposure to particulate matter and neighbourhood deprivation on gestational hypertension

Gestational hypertension, pre-eclampsia and eclampsia are conditions that affect the health of both mothers and infants during and after pregnancy. Recent research indicates the importance of considering environmental, social and individual contributors to poor pregnancy outcomes. Our research examined particulate matter (PM) concentrations as one measure of environmental exposure and neighbourhood quality as one measure of the social environment. We used these measures, as well as maternal characteristics, to predict the risk of gestational hypertension (including pre-eclampsia and eclampsia). North Carolina Detailed Birth Record data for 2000-2003 were obtained and geocoded for all singleton births. Levels of PM(10) and PM(2.5) were determined using air quality data from the US Environmental Protection Agency. Information on a womans residential neighbourhood was determined from 2000 Census data. Modified Poisson regression models clustered by tract were used to examine the associations between PM levels, neighbourhood deprivation and maternal characteristics with gestational hypertension. Analysis was restricted to women residing within 20 km of a PM monitor. Both PM(10) and PM(2.5) were associated with gestational hypertension; the risk ratios for an interquartile range (IQR) increase in exposure were 1.07 [95% confidence interval (CI) 1.04, 1.11] for PM(10) (IQR: 3.92 µg/m(3)) and 1.11 [95% CI 1.08, 1.15] for PM(2.5) (IQR: 2.24 µg/m(3)). Living in a neighbourhood with increased levels of deprivation was also associated with gestational hypertension. Any smoking during pregnancy, younger age and higher level of education were inversely associated with risk of gestational hypertension. Compared with non-Hispanic White women, non-Hispanic Black women were at higher risk of gestational hypertension, whereas Hispanic women were at lower risk. Increased levels of PM and neighbourhood deprivation, as well as certain individual characteristics, were associated with higher risk of gestational hypertension.

Psychosocial differences between smokers and non-smokers during pregnancy.

Despite the well-established adverse birth and childhood health outcomes associated with maternal smoking, smoking rates among pregnant women remain high. Psychosocial health attributes, including anxiety, depression, perceived stress, self-efficacy, and personality characteristics, have especially important roles in smoking behavior. Understanding who smokes during pregnancy and what factors influence this behavior choice may be key to improving the effectiveness of smoking cessation intervention programs. We use data from a prospective cohort study of pregnant women to understand the psychosocial health profiles of women who choose to smoke during pregnancy compared to the profiles of women who do not smoke or successfully quit smoking during pregnancy. Multinomial logistic regression analyses on 1518 non-Hispanic black and non-Hispanic white women assessed the association between smoking status and psychosocial health while controlling for demographic characteristics. Higher levels of perceived stress, depression, neuroticism, negative paternal support, and perceived racism among non-Hispanic blacks were associated with higher odds of being a smoker than a non-smoker (p<0.05). Higher levels of self-efficacy, extraversion, agreeableness, conscientiousness, interpersonal support, positive paternal support, and perceived social standing were associated with lower odds of being a smoker than a non-smoker (p<0.05). Our analysis indicates that women who smoked during pregnancy experienced a more negative constellation of psychosocial adversities than women who did not smoke. Given the psychosocial needs and personality profiles experienced by smokers, more attention to the psychosocial strengths and weaknesses of these women may allow for more tailored smoking cessation programs, enhancing both the short- and long-term effectiveness of such interventions.

Proximity to roadways and pregnancy outcomes

Adverse birth outcomes are associated with exposure to air pollution during pregnancy. Road proximity is a simple, widely available metric for capturing local variation in exposure to traffic-related air pollution. We characterized maternal exposure to traffic-related air pollution during pregnancy using residential proximity to major roadways among 2004–2008 singleton births in NC. Controlling for maternal race, age, education, nativity, marital status, and tobacco use, and season of birth, parity, infant sex, and Census tract-level urbanization and income, we evaluated the association between road proximity and pregnancy outcomes using generalized linear mixed models with a random intercept for each Census tract. Birth weight, birth weight percentile for gestational age, gestational hypertension, and small-for-gestational age were not associated with road proximity; however, women residing within 250 m of a major roadway were at 3–5% increased odds of low birth weight, preterm birth, and late preterm birth compared with women residing beyond 250 m (P<0.05). Our analyses demonstrate an association between proximity to major roadways and pregnancy outcomes using a large sample. Road proximity may represent a relatively straightforward method for assessing maternal risk from exposure to traffic-related air pollution, with results offering guidance for studies that can more accurately characterize air pollution exposures.

Disparities in maternal hypertension and pregnancy outcomes: evidence from North Carolina, 1994-2003.

Objectives. To better understand disparities in pregnancy outcomes, we analyzed data from North Carolina to determine how the pattern of maternal hypertensive disorders differs among non-Hispanic white (NHW), non-Hispanic black (NHB), and Hispanic women across the range of maternal ages. In addition, we explored whether rates of poor birth outcomes, including low birthweight (LBW) and preterm birth (PTB), among hypertensive women differed by race. Methods. We restricted our analyses to births occurring between 1994 and 2003, constructing six five-year maternal age categories: 15–19 years, 20–24 years, 25–29 years, 30–34 years, 35–39 years, and 40–44 years. We used logistic regression to determine the relative contribution of race and age to incidence of maternal hypertension. All analyses controlled for the standard covariates of maternal education, marital status, and tobacco use. To assess the impact of maternal hypertension on birth outcomes, we limited the dataset to women with any hypertensive disorder and used linear regression to determine how particular race-age combinations affected outcomes. We also used logistic regression to find out how particular race-age combinations affected the likelihood of LBW and PTB. Results. The risk of hypertension differed by race, with NHB women exhibiting the highest risk and Hispanic women the lowest risk. Further, rates of hypertension increased with age. Among hypertensive women, pregnancy outcomes differed by race and age, with NHB women having the poorest outcomes (i.e., LBW and PTB) and age exhibiting a dose-response relationship in PTB and very PTB. Conclusions. Patterns of maternal hypertension and subsequent outcomes are important contributors to persistent disparities in pregnancy outcomes.

Assessing exposure metrics for PM and birth weight models.

The link between air pollution exposure and adverse birth outcomes is of public health concern due to the relationship between poor pregnancy outcomes and the onset of childhood and adult diseases. As personal exposure measurements are difficult and expensive to obtain, proximate measures of air pollution exposure are traditionally used. We explored how different air pollution exposure metrics affect birth weight regression models. We examined the effect of maternal exposure to ambient levels of particulate matter <10, <2.5 μm in aerodynamic diameter (PM10, PM2.5) on birth weight among infants in North Carolina. We linked maternal residence to the closest monitor during pregnancy for 2000–2002 (n=350,754). County-level averages of air pollution concentrations were estimated for the entire pregnancy and each trimester. For a finer spatially resolved metric, we calculated exposure averages for women living within 20, 10, and 5 km of a monitor. Multiple linear regression was used to determine the association between exposure and birth weight, adjusting for standard covariates. In the county-level model, an interquartile increase in PM10 and PM2.5 during the entire gestational period reduced the birth weight by 5.3 g (95% CI: 3.3–7.4) and 4.6 g (95% CI: 2.3–6.8), respectively. This model also showed a reduction in birth weight for PM10 (7.1 g, 95% CI: 1.0–13.2) and PM2.5 (10.4 g, 95% CI: 6.4–14.4) during the third trimester. Proximity models for 20, 10, and 5 km distances showed results similar to the county-level models. County-level models assume that exposure is spatially homogeneous over a larger surface area than proximity models. Sensitivity analysis showed that at varying spatial resolutions, there is still a stable and negative association between air pollution and birth weight, despite North Carolinas consistent attainment of federal air quality standards.

Blood Lead Levels Among Pregnant Women: Historical Versus Contemporaneous Exposures

Blood lead among pregnant women, even at modest levels, may impair offspring cognitive development. We examine whether blood lead levels (BLLs) result from current versus historic exposures, among a cohort of pregnant women. Cumulative logit models were used to characterize the relationship between maternal risk factors and higher BLLs. Maternal blood lead levels more likely result from lead remobilization from historic versus contemporaneous exposures. Even if all lead sources were abated immediately, women and their fetuses would experience lead exposure for decades. This work emphasizes the importance of addressing sources of environmental lead exposure in the United States and internationally.

Mercury Levels in an Urban Pregnant Population in Durham County, North Carolina

The adverse effects of prenatal mercury exposure, most commonly resulting from maternal fish consumption, have been detected at very low exposure levels. The omega-3 fatty acids found in fish, however, have been shown to support fetal brain and vision development. Using data from a prospective, cohort study of pregnant women from an inland area in the US South, we sought to understand the fish consumption habits and associated mercury levels across subpopulations. Over 30% of women had at least 1 μg/L of mercury in their blood, and about 2% had blood mercury levels above the level of concern during pregnancy (≥3.5 μg/L). Mercury levels were higher among Asian/Pacific Islander, older, higher educated, and married women. Fish consumption from any source was reported by 2/3 of the women in our study, with older women more likely to consume fish. Despite eating more fish meals per week, lower income, lower educated women had lower blood mercury levels than higher income, higher educated women. This suggests the different demographic groups consume different types of fish. Encouraging increased fish consumption while minimizing mercury exposure requires careful crafting of a complex health message.

Adverse birth outcomes among nulliparous vs. multiparous women.

Objectives. Previous studies indicate that nulliparous women (i.e., women having no previous births) are at higher risk for adverse birth outcomes than multiparous women (i.e., women having had at least one previous birth). We examined whether part of the difference in adverse outcome rates is attributable to nulliparous women with poor pregnancy outcomes being less likely (through choice or fecundity differences) to have a subsequent live birth within the same time period as nulliparous women without adverse outcomes. Methods. Using deterministic matching, we linked nulliparous women from the North Carolina Detailed Birth Record to subsequent births. We employed statistical and simulation-based analyses to estimate first birth outcome rate differences between nulliparous women who did have a subsequent live birth vs. those who did not. Our Markov simulations focused on preterm birth (PTB). Results. Among nulliparous women who were not linked to a second birth, maternal age-adjusted rates of multiple adverse outcomes were all statistically higher compared with rates for linked women. These results also held in race/ethnicity-specific analyses. Simulations found that the relative risk of PTB associated with a history of PTB was underestimated if some women who would have been at risk for PTB did not experience a second birth. Conclusions. The observed differences in rates of adverse outcomes between nulliparous and multiparous women are partly attributable to higher-risk women not having a subsequent live birth, either by choice or due to fecundity differences.