Poor air quality is associated with a considerable proportion of pregnancy loss in India, Pakistan, and Bangladesh, according to a modelling study published in The Lancet Planetary Health journal, which says such losses are more common in north India and Pakistan.
An estimated 349,681 pregnancy losses per year in south Asia were associated with exposure to PM2.5 concentrations that exceeded India’s air quality standard (more than 40 μg/m³), accounting for 7% of annual pregnancy loss in the region from 2000-2016, the study says.
For air pollution above WHO air quality guideline, exposure may have contributed to 29% of pregnancy losses. Although WHO’s guidelines aim for a safer level of air pollution, the authors note that India’s standard is a more realistic target level, given the high average levels of air pollution in the region and the need to balance practical governance and public health.
Considered the first such study to estimate the effect of air pollution on pregnancy loss across the region, it says limitations in the survey data mean that it was unable to distinguish between natural pregnancy loss and abortions, which may have led to an underestimation of the effect of air pollution on natural pregnancy loss.
The researchers included 34,197 women who had lost a pregnancy, including 27,480 miscarriages and 6,717 stillbirths, which were compared to live birth controls. Of the pregnancy loss cases, 77% were from India, 12% from Pakistan, and 11% from Bangladesh.
The authors combined data from household surveys on health from 1998-2016 (from women who reported at least one pregnancy loss and one or more live births) and estimated exposure to PM2.5 during pregnancy through combining satellite with atmospheric modelling outputs.
They created a model to examine how exposure to PM2.5 increased women’s risk of pregnancy loss, calculating risk for each 10 μg/m³ increased in PM2.5 after adjusting for maternal age, temperature and humidity, seasonal variation, and long-term trends in pregnancy loss.
Using this association, they calculated the number of pregnancy losses that may have been caused by PM2.5 in the whole region for the period 2000–16 and looked at how many pregnancy losses might have been prevented under India’s and WHO’s air quality standard (40 μg/m³ and 10 μg/m³, respectively).
Gestational exposure to PM2.5 was associated with an increased likelihood of pregnancy loss, and this remained significant after adjusting for other factors. Each increase in 10 μg/m³ was estimated to increase a mother’s risk of pregnancy loss by 3%, the study says.
Lead study author Tao Xue of Peking University says: “South Asia has the highest burden of pregnancy loss globally and is one of the most PM2.5 polluted regions in the world. Our findings suggest that poor air quality could be responsible for a considerable burden of pregnancy loss in the region, providing further justification for urgent action to tackle dangerous levels of pollution.”