Jennifer D. Parker

Associations between measures of socioeconomic status and low birth weight, small for gestational age, and premature delivery in the United States

We compared associations between five indicators of socioeconomic status (maternal education, paternal education, maternal occupation, paternal occupation, family income) and three reproductive outcomes (low birth weight, small for gestational age, preterm delivery) in a representative sample of US births. We used data from the 1988 National Maternal and Infant Health Survey to estimate odds ratios for relationships between the socioeconomic indicators and birth outcomes, separately by race, after controlling for parity, maternal height, marital status, and maternal age. Nearly all socioeconomic indices were associated with low birth weight among both black and white women. However, there was no consistent pattern between the socioeconomic indices and the other outcomes. Maternal and paternal education levels were the best overall predictors. Magnitudes of association differed between black and white women. To accurately assess the impact of low socioeconomic status on reproductive health, definitions of both status and outcome must be made as explicit as possible.

Maternal exposure to particulate air pollution and term birth weight : a multi-country evaluation of effect and heterogeneity

Background: A growing body of evidence has associated maternal exposure to air pollution with adverse effects on fetal growth; however, the existing literature is inconsistent. Objectives: We aimed to quantify the association between maternal exposure to particulate air pollution and term birth weight and low birth weight (LBW) across 14 centers from 9 countries, and to explore the influence of site characteristics and exposure assessment methods on between-center heterogeneity in this association. Methods: Using a common analytical protocol, International Collaboration on Air Pollution and Pregnancy Outcomes (ICAPPO) centers generated effect estimates for term LBW and continuous birth weight associated with PM10 and PM2.5 (particulate matter ≤ 10 and 2.5 µm). We used meta-analysis to combine the estimates of effect across centers (~ 3 million births) and used meta-regression to evaluate the influence of center characteristics and exposure assessment methods on between-center heterogeneity in reported effect estimates. Results: In random-effects meta-analyses, term LBW was positively associated with a 10-μg/m3 increase in PM10 [odds ratio (OR) = 1.03; 95% CI: 1.01, 1.05] and PM2.5 (OR = 1.10; 95% CI: 1.03, 1.18) exposure during the entire pregnancy, adjusted for maternal socioeconomic status. A 10-μg/m3 increase in PM10 exposure was also negatively associated with term birth weight as a continuous outcome in the fully adjusted random-effects meta-analyses (–8.9 g; 95% CI: –13.2, –4.6 g). Meta-regressions revealed that centers with higher median PM2.5 levels and PM2.5:PM10 ratios, and centers that used a temporal exposure assessment (compared with spatiotemporal), tended to report stronger associations. Conclusion: Maternal exposure to particulate pollution was associated with LBW at term across study populations. We detected three site characteristics and aspects of exposure assessment methodology that appeared to contribute to the variation in associations reported by centers.

Methodological issues in studies of air pollution and reproductive health

In the past decade there have been an increasing number of scientific studies describing possible effects of air pollution on perinatal health. These papers have mostly focused on commonly monitored air pollutants, primarily ozone (O(3)), particulate matter (PM), sulfur dioxide (SO(2)), carbon monoxide (CO), and nitrogen dioxide (NO(2)), and various indices of perinatal health, including fetal growth, pregnancy duration, and infant mortality. While most published studies have found some marker of air pollution related to some types of perinatal outcomes, variability exists in the nature of the pollutants and outcomes associated. Synthesis of the findings has been difficult for various reasons, including differences in study design and analysis. A workshop was held in September 2007 to discuss methodological differences in the published studies as a basis for understanding differences in study findings and to identify priorities for future research, including novel approaches for existing data. Four broad topic areas were considered: confounding and effect modification, spatial and temporal exposure variations, vulnerable windows of exposure, and multiple pollutants. Here we present a synopsis of the methodological issues and challenges in each area and make recommendations for future study. Two key recommendations include: (1) parallel analyses of existing data sets using a standardized methodological approach to disentangle true differences in associations from methodological differences among studies; and (2) identification of animal studies to inform important mechanistic research gaps. This work is of critical public health importance because of widespread exposure and because perinatal outcomes are important markers of future child and adult health.

Fine particulate matter (PM2.5) air pollution and selected causes of postneonatal infant mortality in California.

Studies suggest that airborne particulate matter (PM) may be associated with postneonatal infant mortality, particularly with respiratory causes and sudden infant death syndrome (SIDS). To further explore this issue, we examined the relationship between long-term exposure to fine PM air pollution and postneonatal infant mortality in California. We linked monitoring data for PM ≤2.5 μm in aerodynamic diameter (PM2.5) to infants born in California in 1999 and 2000 using maternal addresses for mothers who lived within 5 miles of a PM2.5 monitor. We matched each postneonatal infant death to four infants surviving to 1 year of age, by birth weight category and date of birth (within 2 weeks). For each matched set, we calculated exposure as the average PM2.5 concentration over the period of life for the infant who died. We used conditional logistic regression to estimate the odds of postneonatal all-cause, respiratory-related, SIDS, and external-cause (a control category) mortality by exposure to PM2.5, controlling for the matched sets and maternal demographic factors. We matched 788 postneonatal infant deaths to 3,089 infant survivors, with 51 and 120 postneonatal deaths due to respiratory causes and SIDS, respectively. We found an adjusted odds ratio for a 10−μg/m3 increase in PM2.5 of 1.07 [95% confidence interval (CI), 0.93–1.24] for overall postneonatal mortality, 2.13 (95% CI, 1.12–4.05) for respiratory-related postneonatal mortality, 0.82 (95% CI, 0.55–1.23) for SIDS, and 0.83 (95% CI, 0.50–1.39) for external causes. The California findings add further evidence of a PM air pollution effect on respiratory-related postneonatal infant mortality.

Family Structure, Socioeconomic Status, and Access to Health Care for Children

OBJECTIVE To test the hypothesis that among children of lower socioeconomic status (SES), children of single mothers would have relatively worse access to care than children in two-parent families, but there would be no access difference by family structure among children in higher SES families. DATA SOURCES The National Health Interview Surveys of 1993-95, including 63,054 children. STUDY DESIGN Logistic regression was used to examine the relationship between the childs family structure (single-mother or two-parent family) and three measures of health care access and utilization: having no physician visits in the past year, having no usual source of health care, and having unmet health care needs. To examine how these relationships varied at different levels of SES, the models were stratified on maternal education level as the SES variable. The stratified models adjusted for maternal employment, childs health status, race and ethnicity, and childs age. Models were fit to examine the additional effects of health insurance coverage on the relationships between family structure, access to care, and SES. PRINCIPAL FINDINGS Children of single mothers, compared with children living with two parents, were as likely to have had no physician visit in the past year; were slightly more likely to have no usual source of health care; and were more likely to have an unmet health care need. These relationships differed by mothers education. As expected, children of single mothers had similar access to care as children in two-parent families at high levels of maternal education, for the access measures of no physician visits in the past year and no usual source of care. However, at low levels of maternal education, children of single mothers appeared to have better access to care than children in two-parent families. Once health insurance was added to adjusted models, there was no significant socioeconomic variation in the relationships between family structure and physician visits or usual source of care, and there were no significant disparities by family structure at the highest levels of maternal education. There were no family structure differences in unmet needs at low maternal education, whereas children of single mothers had more unmet needs at high levels of maternal education, even after adjustment for insurance coverage. CONCLUSIONS At high levels of maternal education, family structure did not influence physician visits or having a usual source of care, as expected. However, at low levels of maternal education, single mothers appeared to be better at accessing care for their children. Health insurance coverage explained some of the access differences by family structure. Medicaid is important for children of single mothers, but children in two-parent families whose mothers are less educated do not always have access to that resource. Public health insurance coverage is critical to ensure adequate health care access and utilization among children of less educated mothers, regardless of family structure.

Air pollution and postneonatal infant mortality in the United States, 1999-2002.

Objective Our goal was to evaluate the relationship between cause-specific postneonatal infant mortality and chronic early-life exposure to particulate matter and gaseous air pollutants across the United States. Methods We linked county-specific monitoring data for particles with aerodiameter of ≤ 2.5 μm (PM2.5) and ≤ 10 μm (PM10), ozone, sulfur dioxide, and carbon monoxide to birth and death records for infants born from 1999 to 2002 in U.S. counties with > 250,000 residents. For each infant, we calculated the average concentration of each pollutant over the first 2 months of life. We used logistic generalized estimating equations to estimate odds ratios of postneonatal mortality for all causes, respiratory causes, sudden infant death syndrome (SIDS), and all other causes for each pollutant, controlling for individual maternal factors (race, marital status, education, age, and primiparity), percentage of county population below poverty, region, birth month, birth year, and other pollutants. This analysis includes about 3.5 million births, with 6,639 postneonatal infant deaths. Results After adjustment for demographic and other factors and for other pollutants, we found adjusted odds ratios of 1.16 [95% confidence interval (CI), 1.06–1.27] for a 10-μg/m3 increase in PM10 for respiratory causes and 1.20 (95% CI, 1.09–1.32) for a 10-ppb increase in ozone and deaths from SIDS. We did not find relationships with other pollutants and for other causes of death (control category). Conclusions This study supports particulate matter air pollution being a risk factor for respiratory-related postneonatal mortality and suggests that ozone may be associated with SIDS in the United States.

The association between childhood asthma prevalence and monitored air pollutants in metropolitan areas, United States, 2001―2004

BACKGROUND Air pollution exposure has been linked to adverse respiratory health outcomes among children, primarily in studies of acute exposures that are often in limited geographic areas. We sought to assess the association between chronic outdoor air pollution exposure, as measured by 12-month averages by county, and asthma among children in metropolitan areas across the nation. METHODS Eligible children included those aged 3-17 years residing in US metropolitan areas who were sampled in the 2001-2004 National Health Interview Survey (N=34,073). 12-month average air pollutant levels for sulfur dioxide, nitrogen dioxide, ozone and particulate matter were compiled by county for 2000-2004. Eligible children were linked to pollutant levels for the previous 12 months for their county of residence. Adjusted odds ratios of having current asthma or an asthma attack in the past 12 months were estimated in single pollutant logistic regression models. RESULTS Children in counties with ozone and, to a less consistent degree, particulate matter levels in the highest quartile were more likely to have current asthma and/or a recent asthma attack than children residing in counties with the lowest pollution levels; the adjusted odds for current asthma for the highest quartile of estimated ozone exposure was 1.56 (95% confidence interval [CI]: 1.15, 2.10) and for recent asthma attack 1.38 (95% CI: 0.99, 1.91). No associations were found with sulfur dioxide or nitrogen dioxide levels. CONCLUSION Although the current US standard for ozone is based on short-term exposure, this cross-sectional study suggests that chronic (12-month) exposure to ozone and particles is related to asthma outcomes among children in metropolitan areas throughout the US.

Comparing exposure metrics in the relationship between PM2.5 and birth weight in California

Although studies suggest that air pollution is linked to perinatal outcomes, the geographic characterization of exposure to pollution differs between the studies. We compared neighborhood- and county-level measures of air pollution exposure, while examining the association between particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) and birth weight among full-term births in California in 2000. To reduce the effects of demographic variability, our analysis was limited to two populations of 8579 non-Hispanic white and 8114 Hispanic mothers who were married, between 20 and 30 years of age, completed at least a high school education, and gave birth for the first time. Measurements from the nearest monitor, and average and distance-weighted average of monitors within a 5-mile radius from each mothers residence (constituting neighborhood metrics) and the mean of monitors within each mothers county of residence were considered. PM2.5 measurements, provided by the California Air Resources Board, were calculated to correspond to each mothers 9-month gestation period. Although metrics within the 5-mile radii and the county were highly correlated (r2=0.78), the county-level metric provided a stronger association between PM2.5 and birth weight (β=−4.04, 95% confidence interval =−6.71, −1.37) than the metric for the average of all monitors within 5-miles (β=−1.38, 95% confidence interval =−3.36, 0.60) among non-Hispanic white mothers; similar results were observed among the Hispanic sample of mothers. Consequently, inferences from studies using different definitions of air pollution exposure may not be comparable.

Air Pollution and Childhood Respiratory Allergies in the United States

Background Childhood respiratory allergies, which contribute to missed school days and other activity limitations, have increased in recent years, possibly due to environmental factors. Objective In this study we examined whether air pollutants are associated with childhood respiratory allergies in the United States. Methods For the approximately 70,000 children from the 1999–2005 National Health Interview Survey eligible for this study, we assigned between 40,000 and 60,000 ambient pollution monitoring data from the U.S. Environmental Protection Agency, depending on the pollutant. We used monitors within 20 miles of the child’s residential block group. We used logistic regression models, fit with methods for complex surveys, to examine the associations between the reporting of respiratory allergy or hay fever and annual average exposure to particulate matter ≤ 2.5 μm in diameter (PM2.5), PM ≤ 10 μm in diameter, sulfur dioxide, and nitrogen dioxide and summer exposure to ozone, controlling for demographic and geographic factors. Results Increased respiratory allergy/hay fever was associated with increased summer O3 levels [adjusted odds ratio (AOR) per 10 ppb = 1.20; 95% confidence interval (CI), 1.15–1.26] and increased PM2.5 (AOR per 10 μg/m3 = 1.23; 95% CI, 1.10–1.38). These associations persisted after stratification by urban–rural status, inclusion of multiple pollutants, and definition of exposures by differing exposure radii. No associations between the other pollutants and the reporting respiratory allergy/hay fever were apparent. Conclusions These results provide evidence of adverse health for children living in areas with chronic exposure to higher levels of O3 and PM2.5 compared with children with lower exposures.

Preterm birth after the Utah Valley Steel Mill closure: a natural experiment.

Background: Prior studies have linked the Utah Valley Steel Mill closure that took place between August 1986 and September 1987 to improvements in several health outcomes. So-called natural experiments ease concerns over confounding and exposure misclassification, concerns that are common in studies of air pollution and pregnancy outcome. Methods: We compare birth outcomes for Utah mothers within and outside the Utah Valley, before, during, and after the mill closure. Results: Mothers who were pregnant around the time of the closure of the mill were less likely to deliver prematurely than mothers who were pregnant before or after; effects were strongest for exposure during the second trimester. Preterm birth within the Utah Valley did not change during the time of mill closure. No patterns for birth weight were observed. Conclusions: These results support other studies that have found effects on preterm birth of air pollution exposure early in pregnancy.