Air pollution released from the burning of fossil fuels may be linked to an uptick in miscarriages, a new study has found.
This research comes on the heels of a separate review study that found air pollution exposure during pregnancy may be linked to greater risk of children developing autism.
The new study investigated exposure to fine particulate mater, sulfur dioxide and nitrogen dioxide in pregnant woman during their first trimester.
These toxic chemicals are found all throughout the US, but they are particularly prevalent in cities such as Bakersfield and Los Angeles, California, Fairbanks, Alaska and Phoenix, Arizona.
The researchers gathered data from air quality monitoring stations in Baoji, a city in northwestern China, recorded between 2017 and 2019.
They then analyzed these records alongside data on 770 pregnant women who were admitted to two of the city’s hospitals between 2018 and 2019.
Among them, 154 suffered miscarriages, and the researchers found that a significant number of those who lost their baby were pregnant while air quality was poorest in Baoji.
There are several theories for why air pollution may cause miscarriage, including disruption of pregnancy hormones, triggering harmful inflammation in the mother and negative impacts on fetal development.
Researchers have uncovered a link between three common air pollutants and miscarriages
Fine particulates, sulfur dioxide and nitrogen dioxide are three of the six ‘criteria’ pollutants, so called because the Environmental Protection Agency (EPA) regulates them by developing criteria for setting permissible levels.
Burning fossil fuels is one of the main sources for all three of these pollutants. Long-term exposure to them can lead to lung disease, heart disease and premature death.
Recently, a review of the latest literature published in the journal Brain Medicine found that people with a genetic predisposition to autism who were exposed to air pollution in early life were more likely to develop the condition than people exposed to less air pollution.
Researchers from Yan’an University in China investigated whether these pollutants might impact the incidence of miscarriage in pregnant women.
Air quality in Baoji is generally considered poor, but it varies seasonally due to increased coal burning for home heating in winter, the researchers stated in their report.
As of November 12, the air quality index (AQI) in Baoji is 229, which is considered ‘very unhealthy,’ according to IQAir. By comparison, Los Angeles currently has an AQI of 18, which is considered ‘good.’
But both Los Angeles and Baoji share the same main pollutant: fine particulates.
These microscopic particles can travel deep inside the lungs, causing tissue damage and inflammation.
The study found that women who were pregnant in spring and winter – when concentrations of certain air pollutants were higher in Baoji – more commonly suffered miscarriages
The researchers analyzed air pollution records alongside data on 770 pregnant women admitted to the Department of Obstetrics and Gynecology of Baoji Central Hospital and Baoji People’s Hospital from 2018 to 2019.
Of these 770 women, aged 19 to 44, 154 suffered miscarriages and 616 delivered full-term babies.
The researchers calculated the level of outdoor air pollution exposure for each pregnant woman during their first trimester.
They published their findings in the journal Nature on Monday.
They study found that those who were pregnant in spring and winter had a higher incidence of miscarriage than those who were pregnant in summer and autumn, which could be good evidence of a link between fine particulates, sulfur dioxide, nitrogen dioxide and miscarriage, they wrote.
That’s because the air quality monitoring data revealed that concentrations of these pollutants were higher in spring and winter than in summer and autumn, as residents of Baoji burn coal to heat their houses in the colder months.
The study did not find a link between ozone or inhalable particles and miscarriage.
These new findings are in line with a 2016 study that found that exposure to nitrogen dioxide alone can increase miscarriages by 16 percent.
Experts have proposed several explanations for why air pollution may increase risk of miscarriage.
Some suggest that it is because these chemicals disrupt pregnancy hormones, while others point to their ability to trigger harmful inflammation in pregnant women.
Other studies have found that air pollutants can affect fetal development and lead to low birth weight, preterm birth, birth defects, abnormal fetal growth rate and neonatal mortality.
Research has also found that air pollution can cause abnormal placental development which can lead to adverse pregnancy outcomes.
But there are many other risk factors for miscarriage, and not all of them are environmental factors like pollution.
Age, history of miscarriage, vaginal microbiome, genetics and immune factors are all known to influence miscarriage risk, the researchers wrote.
Their study evaluated these independently of air-pollution exposure, and found that occupation, number of past deliveries and C-sections, last menstrual season, history of pregnancy complications and pregnancy comorbidities were significant risk factors for miscarriage.
While this study has identified a notable link between three widespread air pollutants and miscarriages, it has not found that breathing air pollution causes miscarriages.
To further investigate this link and a potential causal relationship, future studies will need to take indoor air pollution into account and use a much larger sample size of pregnant women, the researchers wrote.
And to look for stronger evidence of causality, future studies should take a prospective approach – tracking mothers and miscarriage incidence throughout their pregnancies.
