Elsevier

Environment International

Volume 117, August 2018, Pages 226-236
Environment International

Associations between birth outcomes and maternal PM2.5 exposure in Shanghai: A comparison of three exposure assessment approaches

https://doi.org/10.1016/j.envint.2018.04.050Get rights and content

Highlights

  • We assessed PM2.5 exposure, accounting for missing data, at 1-km resolution.

  • Maternal PM2.5 exposure was associated with decreased birth weight.

  • Maternal PM2.5 exposure was associated with increased risk of preterm birth.

  • The magnitude of the estimated associations is higher than precious findings.

  • Satellite based exposure assessment without accounting for missing data led to bias.

Abstract

Background

Few studies have estimated effects of maternal PM2.5 exposure on birth outcomes in China due to the lack of historical air pollution data.

Objectives

We estimated the associations between maternal PM2.5 exposure and birth outcomes using gap-filled satellite estimates in Shanghai, China.

Methods

We obtained birth registration records of 132,783 singleton live births during 2011–2014 in Shanghai. PM2.5 exposures were assessed from satellite-derived estimates or central-site measurements. Linear and logistic regressions were used to estimate associations with term birth weight and term low birth weight (LBW), respectively. Logistic and discrete-time survival models were used to estimate associations with preterm birth. Effect modification by maternal age and parental education levels was investigated.

Results

A 10 μg/m3 increase in gap-filled satellite-based whole-pregnancy PM2.5 exposure was associated with a −12.85 g (95% CI: −18.44, −7.27) change in term birth weight, increased risk of preterm birth (OR 1.27, 95% CI: 1.20, 1.36), and increased risk of term LBW (OR 1.22, 95% CI: 1.06, 1.41). Sensitivity analyses during 2013–2014, when ground PM2.5 measurements were available, showed that the health associations using gap-filled satellite PM2.5 concentrations were higher than those obtained using satellite PM2.5 concentrations without accounting for missingness. The health associations using gap-filled satellite PM2.5 had similar magnitudes to those using central-site measurements, but with narrower confidence intervals.

Conclusions

The magnitude of associations between maternal PM2.5 exposure and adverse birth outcomes in Shanghai was higher than previous findings. One reason could be reduced exposure error of the gap-filled high-resolution satellite PM2.5 estimates.

Introduction

Preterm birth and low birth weight have been widely documented as significant predictors of infant mortality and have negative long-term effects in adulthood (CDC, 2002; Rogers and Velten, 2011; Swamy, 2011). Liu et al. (2015) estimated that in 2013, preterm birth ranked as the leading cause of death before age 5 and was responsible for 15.4% (0.965 million) of deaths before age 5 globally. Adverse birth outcomes in association with maternal exposure to PM2.5 (fine particulate matter with an aerodynamic diameter of 2.5 μm or less) have been studied in various populations (Li et al., 2017; Polichetti et al., 2013). While results from recent meta-analyses support the link between maternal PM2.5 exposure and adverse birth outcomes, substantial heterogeneity in health effect estimates exists among different studies (Sun et al., 2015; Sun et al., 2016). This heterogeneity is partly due to differences in exposure assessment methods, and the authors reported that studies assessing individual-level exposures tended to report stronger associations relative to studies assessing regional-level exposures. In addition, similar to many other health endpoints reported in the literature, the overwhelming majority of the included studies in these meta-analyses were conducted in the U.S. where PM2.5 levels are relatively low. Studies in highly polluted regions such as China can further elucidate the magnitude of PM2.5-associated health effects at high exposure levels. However, ground measurements of PM2.5 concentrations are often very sparse or nonexistent in most part of the developing world. For countries where the air quality monitoring network was established recently, lack of long-term measurements remains an obstacle to studying the association between adverse birth outcomes and exposure to PM2.5. Additionally, measurements from ground central monitors have limited spatial representativeness. Previous studies used specific buffers, ranging from 6.4 km to 50 km in radius, around monitoring stations to select study populations and assign exposure, with the intent of reducing exposure error (Chang et al., 2011; Darrow et al., 2011; Hyder et al., 2014). However, this method reduces sample size, and an optimal cutoff distance is difficult to determine.

To assess historical air pollution levels and characterize local-scale variability in air pollution, satellite-retrieved aerosol optical depth (AOD) has been used to predict ground PM2.5 concentrations during the past decade (Seltenrich, 2014). Polar-orbiting satellites have global coverage, long data records, and high spatiotemporal resolution, but missingness in satellite data has raised concerns regarding its use in epidemiological studies. Annually, 30 to 70% satellite retrievals can be missing due to cloud cover and high surface reflectance in East Asia (Xiao et al., 2016). Unfortunately, situations that lead to failed satellite retrievals often influence the production and deposition of PM2.5, e.g. cloud cover leads to reduced photochemical reactions. Thus, using satellite predictions without accounting for the non-random missingness may result in exposure misclassification. Strickland et al. (2016) evaluated the influence of missing satellite-derived PM2.5 predictions on the association between short-term PM2.5 exposure and pediatric emergency department visits in Georgia, US. They reported that, in general, a large proportion of missing satellite predictions tended to overestimate regional average PM2.5 exposure compared with ground measurements and led to lower health association estimates. To date, studies on the influence of missing satellite data on PM2.5 longer-term exposure assessment are very limited.

We developed a gap-filling method that provided full-coverage daily PM2.5 predictions at 1-km resolution using the Multi-Angle Implementation of Atmospheric Correction (MAIAC) aerosol product (Xiao et al., 2017). In this study, we analyzed the associations between birth outcomes (birth weight and preterm birth) and maternal PM2.5 exposure in Shanghai, China, during 2011–2014, and compared the estimated health effects using three exposure metrics: satellite predictions with missingness, gap-filled satellite predictions with complete coverage, and measurements from ground central monitors.

Section snippets

Data and outcome assessments

Shanghai is located on the east coast of China (Fig. A.1) and is one of the largest cities in the world with >24 million residents. Benefiting from the establishment of a special economic zone in 1993, Pudong New Area as well as Shanghai has become one the most economically developed regions in China as well as in East Asia. Birth registration data for live births between January 1st, 2011 and December 31st, 2014 were obtained from Pudong New Area Centers for Disease Control and Prevention

Results

The annual average PM2.5 concentrations from satellite predictions and central-site measurements in 2014 are shown in Fig. 1. PM2.5 concentrations decreased from west to east. Characteristics of the study population are shown in Table 1. The mean birth weight among term births was 3389 g, with a standard deviation of 403 g. The preterm birth rate in Shanghai during 2011–2014 was 4.41% and the term LBW rate was 0.95%. Previous studies reported higher preterm birth rate in China (4.8%) during

Discussion

In this study, we observed associations between maternal PM2.5 exposure during all exposure windows and adverse birth outcomes, including decreased birth weight, increased risk of term LBW, and increased risk of preterm birth in a highly polluted region. Exposure assessment approaches affected the estimated health effects, and satellite based exposures that did not account for missing data led to lower magnitude health effect estimates. Maternal age and parental education levels appeared to

Conclusions

We reported decreased birth weight as well as increased risk of preterm birth and term LBW in association with maternal PM2.5 exposure in Shanghai, China, from 2011 to 2014. The magnitude of associations between maternal PM2.5 exposure and birth outcomes was slightly higher than previously reported findings. Health association estimates were influenced by exposure assessment approaches, and when using satellite predictions for exposure assessment, researchers should account for missing data. We

Acknowledgments

This work was supported by the National Institutes of Health [grant number R01ES027892]; the Public Welfare Research Program of National Health and Family Planning Commission of China [grant number 201502003]; and the General Program of Health Bureau of Shanghai Pudong New Area [grant number PW2016A-6].

The authors have no conflict of interest to declare.

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