Estimation of stillbirths attributable to ambient fine particles in 137 countries

Gestational exposure to ambient fine particles (PM2.5) increases the risk of stillbirth, but the related disease burden is unknown, particularly in low- and middle-income countries (LMICs). We combine state-of-the-art estimates on stillbirths, and multiple exposure–response functions obtained from previous meta-analyses or derived by a self-matched case-control study in 54 LMICs. 13,870 stillbirths and 32,449 livebirths are extracted from 113 geocoded surveys from the Demographic and Health Surveys. Each stillbirth is compared to livebirth(s) of the same mother using a conditional logit regression. We find that 10-µg/m3 increase of PM2.5 is associated with an 11.0% (95% confidence interval [CI] 6.4, 15.7) increase in the risk of stillbirth, and the association is significantly enhanced by maternal age. Based on age-specific nonlinear PM2.5–stillbirth curves, we evaluate the PM2.5-related stillbirths in 137 countries. In 2015, of 2.09 (95% CI: 1.98, 2.20) million stillbirths, 0.83 (0.54, 1.08) million or 39.7% (26.1, 50.8) are attributable to PM2.5 exposure exceeding the reference level of 10 μg/m3. In LMICs, preventing pregnant women from being exposed to PM2.5 can improve maternal health.


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There were no sex-and gender-based analyses have been performed.
We analyzed 46,319 cases of gestation linked to 13,870 mothers from 1998 to 2016. The mean maternal age in the control group was 24.97 years with a standard deviation (SD) of 6.02 years, younger than the stillbirth group (mean 26.56 years; SD 7.02 years). The mean length of intervals between stillbirth and livebirth was 3.81 (SD = 2.45) years.
This study is an observational study based on the extent data collected by DHS fieldworkers. We utilized all available samples from the DHS database.
NA. This study is based on publicly available population data. We adhered to the DHS data usage guidelines in all our analyses. No further ethic approval is required.
We developed age-specific exposure-response curves to assess the global risk assessment on PM2.5-related stillbirths. We combined state-of-the-art estimates on key inputs, namely, (1) total number of stillbirths by country, (2) gridded PM2.5 concentrations, (3) gridded demographic variables on total pregnancies and sex-age-specific populations, and (4) multiple exposure-response functions obtained from previous meta-analyses or derived by a self-matched case-control study of individual-level reproductive histories from 54 low-and middle-income countries.
Valid records of pregnancy outcomes were obtained from the Demographic and Health Surveys (DHS) program from 1998 to 2016. All eligible samples aged 15-49 years old from 54 LMICs were finally involved in our study.
This study was based on extant DHS database. For each mother, to minimize recall bias, we incorporated only the most recent case of pregnancy loss and all available controls in the study period. No further sampling procedure was conducted.
The DHS surveys are household-based instruments, and the samples were selected using a complex two-stage design. The females of reproductive age (15-49 years) in each household were of particular interest, and their records for socioeconomic status, fertility, reproductive history, infant mortality, etc. were screened by well trained interviewers using standard questionnaires. DHS utilized a team approach to data collection. Usually, each DHS team is composed of a supervisor, field editor, and several interviewers. The cases are recorded by the interviewers using the reproductive module of the uniform questionnaire. The geographic information are recorded by the Global Position System (GPS) device.
To estimate the exposure-response curves, we included all eligible samples during the period (i.e., 1998 -2016) from 113 geocoded surveys of 54 low-and middle-income countries. To combine the curves with state-of-the-art estimates on the population at risk, PM2.5 concentration, and baseline risk, we evaluated the number of stillbirths attributable to PM2.5 exposure in 137 countries from 2000 to 2019.
For each mother, we incorporated only the most recent case of pregnancy loss and all available controls in the study period. No data were excluded.
All attempts to repeat the experiment were successful.
NA. This study is an observational study, and we didn't perform further sampling or randomizing.
This study is an observational, and thus is not applicable for a blinding design.