Air pollution causes more pregnancy losses in India than Pakistan and Bangladesh, says study

Researchers estimated exposure to high concentration of PM 2.5 during pregnancy by combining satellite images with atmospheric modelling outputs

PTI photo
PTI photo

Biswajeet Banerjee

Air pollution, which accounts for 7 per cent annual pregnancy loss in the region, causes more miscarriages and stillbirths in India than in Pakistan and Bangladesh because of exposure to high concentration of PM 2.5 in the air.

As per a modelling study published in ‘The Lancet Planetary Health’ journal, there were 34,197 women who had a pregnancy loss, including 27,480 miscarriages and 6,717 stillbirths. 77% of these cases were from India compared to 12% from Pakistan and 11% from Bangladesh, the study said.

Although the total burden of pregnancy loss was predominantly borne by rural women aged under 30 years old in recent years, the burden attributable to high levels of PM 2.5 also affected older mothers (aged 30 years or over) in rural areas because of their high susceptibility to its adverse effects.

The lead author of the study, Dr. Tao Xue of Peking University, China, says, “South Asia has the highest burden of pregnancy loss globally and is one of the most PM 2.5 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.”

Researchers estimated exposure to high concentration of PM 2.5 during pregnancy by combining satellite images with atmospheric modelling outputs. They found that the pregnancy loss associated with air pollution was more common in the northern plain region in India and Pakistan.

To carry out their analysis, 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 high concentration of PM 2.5 during pregnancy by combining satellite with atmospheric modelling outputs. They created a model to examine how exposure to high concentration of PM 2.5 increased women’s risk of pregnancy loss, calculating risk for each 10 μg/m³ increase 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 high concentration of PM 2.5 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).

Dr Surya Kant, Professor and Head, Department of Respiratory Medicine in King George’s Medical University, Lucknow, said PM 2.5 are very small particles that cause lung disease (asthma) and heart diseases. In many cases exposure to high concentration of PM 2.5 leads to miscarriages or stillbirth, he said.

“Pregnant women who were exposed to air pollutants such as particulate matter (PM) 2.5, Sulfur Dioxide (SO2), Ozone (O3) and Carbon Monoxide (CO) suffered missed abortion in the first trimester (MAFT) or missed miscarriage,” Dr Surya Kant said.

Pollutants penetrating the bloodstream of a foetus might interact with its tissue components to produce pathological effects, leading to irreversible damage to the dividing cells of the foetus and triggering hypoxic harm or immune mediated injury during critical periods of development.

MAFT occurs when a foetus stops growing or has died, but there are no physical symptoms such as bleeding or pain. It takes place before 12 weeks of gestation and women are often unaware that their pregnancy has ended.

One of the co-authors of the Lancet study, Dr. Tianjia Guan, says: “We know losing a pregnancy can have knock-on mental, physical and economic effects on women, including increased risk of postnatal depressive disorders, infant mortality during subsequent pregnancy, and increase the costs related to pregnancy, such as loss of labour. Therefore, reducing pregnancy loss may also lead to knock-on improvements in gender equality.”

Previous studies have suggested a link between air pollution and pregnancy loss in other regions, but this is the first study to quantify the burden in south Asia, which is the most populous region in the world and has the highest rate of pregnancy loss. “Therefore, understanding the risk factors for pregnancy loss in south Asia is crucial to improving maternal health regionally and globally,” the study said.

From 2000 to 2016, 349,681 pregnancy losses per year were associated with ambient exposure to air pollution exceeding India’s air quality standard — accounting for 7% of the total annual pregnancy loss burden in this region. 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. The authors note several limitations of their study. In the surveys, they were not able to distinguish between natural pregnancy loss and abortions and there was under-reporting of pregnancy losses because of stigma or ignoring very early pregnancy losses. In addition, satellite-based estimates of PM 2.5 were used, which was necessary because insufficient local monitoring is available.

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