Estimating birthweight reduction attributable to maternal ozone exposure in low- and middle-income countries

Omitted variable bias in single-pollutant epidemiological models for estimating long-term health effects of ambient fine particulate matter and ozone

Long-term exposure to PM2.5 and O3 is linked to various adverse health outcomes. However, many epidemiological studies on their health effects use single-pollutant models, leading to omitted variable bias (OVB). The percent bias, based on the classical OVB formula, depends on the PM2.5-O3 correlation and unobservable true effects. Data were sourced from two recent meta-analyses of the log-linear link between all-cause mortality and per-unit exposure to PM2.5 or O3. We then developed a new meta-regression method to correct biases, and its performance was verified through simulation. The OVB for PM2.5 or O3 can vary greatly from positive to negative across different spatial scales (like country, sub-national region, or city). By applying this method to 24 individual estimates, we found that a 10 μg/m³ increase in PM2.5 was linked to a 7.4 % increase in all-cause mortality risk, while O3's association with all-cause mortality was not significant, which implies that PM2.5 must be considered in epidemiological analyses to obtain reliable effect estimates for O3. Our findings offer novel methodologies for the systematic assessment of the health effects of multiple pollutants. This contribution holds significant potential in fortifying health intervention strategies and minimizing the health risks posed by air pollution to the public.

Health effects associated with ozone in China: A systematic review

As the ozone (O3) pollution becomes severe in China, it poses a threat to human health. Currently, studies on the impacts of O3 on different regions and groups are limited. This review systematically summarizes the relationship between O3 pollution and mortality and morbidity across the nation, regions, and cities in China, with a focus on the regional and group-specific studies. Then, we clarify the overall limitations in the research data, methods, and subjects. In addition, we briefly discuss the mechanisms by which O3 exposure affects human health, analyzing the effects of O3 on human health under heatwaves (temperature) condition, multi-pollutant modeling, and future climate scenarios. Finally, we give some suggestions for future research directions. Studies found that increased risks of premature mortality and morbidity of respiratory and cardiovascular diseases are closely associated with high concentration O3 exposure. Besides, the old and children are sensitive groups, more studies are needed estimate the risk of their health associated with O3 pollution. Severe O3 pollution in Northern and Eastern China, has significantly increased premature mortality. O3 pollution has led to decreased lung function in the elderly in East China, and a higher asthma risk among young people in South China. Comparing with other regions, less research studied the relationship between O3 pollution and health of local people in Southwest, Central, Northeast, and Northwest Regions. Therefore, it is necessary to enhance research in these regions, with a particular emphasis on the distinctive health consequences of O3 pollution in these regions. Given the diversity of regions and research groups, comprehensive comparison is crucial for determining the impact of O3 pollution on human health in China.

Estimating avoidable burden of stillbirth attributable to greenness improvement in Iran

INTRODUCTION

Expanding evidence suggests beneficial impacts of greenspace on human health, yet the relationships between greenness and stillbirth remain unknown. This study aimed to quantify the risk and burden of stillbirth associated with maternal greenness exposure during pregnancy.

METHODS

A total of 3,982,304 eligible birth records across 31 provinces in Iran from 2013 to 2018 were included in this study. Greenness exposure during pregnancy was assessed using the satellite-based normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) with multiple buffers. Stillbirth was defined as the birth of babies with no signs of life at ≥22 weeks of gestation. Multivariable-adjusted logistic regression models were employed to investigate greenness-stillbirth associations. To estimate the exposure-response functions, greenness exposures were fitted as smooth terms using restricted cubic splines. Avoidable burden of stillbirth under the predefined scenarios of improved greenness was estimated through a counterfactual analysis.

RESULTS

A total of 29,770 stillbirths occurred during 2013-2018, totaling to an overall annual rate of 748 cases per 100,000 births. Lower stillbirth risks were consistently seen in pregnant mothers being exposed to greater greenness within buffers of 500-3000 m. For instance, per 0.1-unit increase of NDVI and EVI within a 3000-m buffer was associated with the estimated odds of 0.971 (95 % confidence interval: 0.963-0.978) and 0.957 (0.947-0.968) for stillbirth, respectively. Evidently nonlinear relationships were identified between greenness exposure and stillbirth, exhibiting approximately an inverted L-shaped pattern with the steeper slope at high greenness levels. Assuming causality, 34-41 stillbirths per 100,000 births could be avoidable by achieving the 80th percentile of NDVI/EVI during 2013-2018, representing 4.6-5.4 % of nationwide registry-based stillbirths in Iran.

CONCLUSIONS

Our findings provided robust national evidence on beneficial effects of surrounding greenness in alleviating risk and burden of stillbirth in Iran, suggesting a greener environment could potentially serve as a promising intervention strategy for reducing stillbirth risk in less developed countries.

Estimating the Risk of Women Anemia Associated with Ozone Exposure Across 123 Low- and Middle-Income Countries: A Multicenter Epidemiological Study

Anemia in women of reproductive age (WRA) presents a pressing global public health issue, particularly in low- and middle-income countries (LMICs). Yet, the potential impact of ozone (O3) exposure on anemia remains uncertain. The study included 1,467,887 eligible women from 83 surveys of 45 LMICs between 2004 to 2020. Monthly O3 exposure was estimated using machine learning, with the year preceding the survey as the primary exposure window. Fixed-effects models evaluated the association between O3 and anemia. An exposure-response function (ERF) was constructed using a varying-coefficient regression model, and then extrapolated to estimate the anemia burden in relation to O3 in 123 LMICs. In the fully adjusted regression model, each 10 ppb increase in annual O3 concentration was associated with an 8% elevation in anemia risk. The nonlinear ERF indicated a threshold effect of O3 on anemia at approximately 47.2 ppb. In 2020, more than 7.6 million anemic WRA (1.58%) in 123 LMICs were associated with O3 exposure. The potentially attributable burden has generally decreased from 2004 to 2020, notably in South Asia. Our findings highlight the importance of air pollution mitigation in LMICs to address anemia disparities among women.

Spatio-temporal distribution and socioeconomic inequality of low birthweight rate in China from 1992 to 2021 and its predictions to 2030

This paper aims to investigate the trend, spatio-temporal distribution, and socioeconomic inequality of the low birthweight rate (LBWR) in China from 1992 to 2021 and to project the LBWR to 2030. We performed a secondary analysis of data from the China Health Statistics Yearbook. LBWR refers to the ratio of the number of infants born with a birth weight less than 2,500 grams to the number of live births in a given year. We used joinpoint regression models to estimate LBWR trends from 1992 to 2021 for the whole country and from 2002 to 2021 for the three regions (eastern, central, and western regions) and each province. The slope index of inequality (SII) and relative index of inequality (RII) were calculated for each year from 2002 to 2021 based on provincial data. LBWR increased from 2.52% (1992) to 3.70% (2021), and the average annual percentage change (AAPC) (95% confidence interval [CI]) was 1.35% (0.22%, 2.49%) in China. The overall LBWR from 2002 to 2021 was greatest in the Eastern region, but LBWR had the fastest increase in the Western region, with an AAPC (95% CI) of 3.15% (2.59%, 3.12%). There were spatio-temporal differences in the LBWR and trends between provinces. The SII and RII increased linearly from -0.15 and 0.94 to 0.53 (B = 0.035%, p < 0.001) and 1.16 (B = 0.011, p < 0.01), respectively, over the past 20 years. The results of the ARIAM model showed that the National LBWR will be increasedfrom 3.70% in 2021 to 5.28% in 2030. The LBWRs in the eastern, central and western regions in 2030 will be 4.93%, 6.02% and 5.82%, respectively. National and local governments must prioritize disadvantaged groups to mitigate the rapid prevalence of LBWR, reduce regional disparities, and improve perinatal and infant health and health equity in China.

Association between pre-pregnancy maternal stress and small for gestational age: a population-based retrospective cohort study

BACKGROUND

Maternal stress is a potential factor affecting fetal growth, but it is unknown whether it directly affects fetal growth restriction. This study aims to investigate the association between pre-pregnancy maternal stress with small for gestational age (SGA).

METHODS

This study used a population-based retrospective cohort analysis to examine the association between pre-pregnancy maternal stress and SGA in offspring. Data were extracted from the National Preconception Health Care Project (NPHCP), conducted between 2010 and 2012, which encompassed preconception health-related information from 572,989 individuals across various regions in China. Logistic regression models were used to assess the associations between pre-pregnancy maternal stress variables and the risk of SGA. In addition, Synthetic Minority Over-sampling Technique (SMOTE) and Propensity Scores (PS) methods were used to enhance the model's ability to the associations between pre-pregnancy maternal stress and SGA.

RESULTS

Pre-pregnancy maternal stress was significantly associated with an increased the risk of SGA in offspring (OR 1.35, 95% CI 1.20 to 1.51, P < 0.001). Stress related to life and economic factors notably increased the risk of SGA across different socio-economic conditions, whereas stress related to friends did not show a statistically significant association (P > 0.05). Specially, individuals with lower socio-economic status that characterized by below high school education levels (OR = 1.45, 95% CI: 1.23 to 1.70), farmer occupation (OR = 1.33, 95% CI: 1.15 to 1.55, P = 0.002), rural residence (OR = 1.38, 95% CI: 1.22 to 1.56, P < 0.001), and younger age (under 35 years: OR = 1.35, 95% CI: 1.20 to 1.52, P < 0.001) were more susceptible to pre-pregnancy maternal stress, increasing their risk of SGA.

CONCLUSIONS

Pre-pregnancy maternal stress was positively associated with an increased risk of SGA in offspring. Individuals with lower socio-economic status were more likely to experience pre-pregnancy maternal stress related to life and economic factors, which in turn contributed to a higher risk of SGA.

Maternal ozone exposure lowers infant's birthweight: A nationwide cohort of over 4 million livebirths in Iran

BACKGROUND

Nationwide evidence linking maternal ozone exposure with fetal growth restriction (FGR) was extensively scarce, especially in the Middle East with dry climate and distinct religious culture.

METHODS

We carried out a national retrospective birth cohort study using registry-based records from 749 hospitals across 31 provinces in Iran from 2013 to 2018. Monthly concentrations of maximum daily average 8-hour (MDA8) ozone at 0.125° × 0.125° resolution were extracted from well-validated spatiotemporal grid dataset. Linear and logistic regression models were employed to evaluate associations of maternal MDA8 ozone exposure with birthweight outcomes. Assuming causality, the comparative risk assessment framework was utilized to estimate the burden of low birthweight (LBW), small for gestational age (SGA), and birthweight loss per livebirth (BLL) attributable to ambient ozone pollution.

RESULTS

Of 4030383 livebirths included in the study, 264304 (6.6%) were LBW and 484405 (12.0%) were SGA. Each 10-ppb increase in MDA8 ozone exposure was associated with an odds ratio of 1.123 (95% confidence interval [CI]: 1.104 to 1.142) for LBW and 1.210 (95% CI: 1.197 to 1.223) for SGA, and a 30.5-g (95% CI: 29.0 to 32.0) reduction in birthweight. We observed approximately linear exposure-response relationships of maternal MDA8 ozone exposure with LBW (Pnonlinear= 0.786), SGA (Pnonlinear= 0.156), and birthweight reduction (Pnonlinear= 0.104). Under the premise of causal association, we estimated 6.6% (95% CI: 5.7 to 7.5) of LBW, 10.1% (95% CI: 9.6 to 10.6) of SGA, and 18.8 g (95% CI: 17.9 to 19.7) of BLL could be attributable to maternal ozone exposure in Iran. Considerably greater risk and burden of ozone-related FGR were observed among younger, less-educated, and rural-dwelling mothers.

CONCLUSIONS

Our study provided compelling evidence that maternal ozone exposure was associated with heightened FGR risk and burden, particularly among socioeconomically disadvantaged mothers. These findings underscored the urgent need for government to incorporate socioeconomic factors into future ozone-related health policies, not only to mitigate pollution, but also minimize inequality.

Stillbirths Associated with Particle Pollution are Disproportionally Contributed by Sand Dust: Findings from 52 Low- and Middle-Income Countries

Whether maternal exposure to dust-sourced particulate matter (hereafter, dust PM2.5) is associated with stillbirth remains unknown. We adopted a sibling-matched case-control design to analyze 9332 stillbirths and 17,421 live births. We associated the risk of stillbirth simultaneously with dust and nondust components of PM2.5 and developed a nonlinear joint exposure-response function. Next, we estimated the burden of stillbirths attributable to the PM2.5 mixture. The concentration index was used to evaluate whether the burden of PM2.5-related stillbirths was disproportionally distributed among pregnancies exposed to dust-rich particles. Each 10 μg/m3 increase in dust PM2.5 was associated with a 14.5% (95% confidence interval: 5.5, 24.2%) increase in the odds of stillbirth. Based on the risk assessment across 137 countries, sand dust contributed to about 15% of the PM2.5 exposure but to about 45% of the PM2.5-related stillbirths during 2003-2019. In 2015, 30% of the PM2.5-related stillbirths were concentrated within 15% of pregnancies exposed to the dust-richest PM2.5. The index increased in subregions, such as South Asia, suggesting the growth of health inequality due to exposure to dust PM2.5. Based on our findings, land management, such as halting desertification, will help prevent stillbirths and reduce global maternal health inequality.