Air quality has been associated with numerous adverse health outcomes, from asthma to diabetes to pre-term birth. Several recent studies have suggested that maternal exposures to air pollution and temperature extremes might contribute to low birth weight (LBW), preterm birth (PTB), and other outcomes that can adversely affect infant health. Researchers at University of Utah Health found women living along the Wasatch Front — the most populous region in the state of Utah — had a higher risk (16%) of miscarriage following short-term exposure to elevated air pollution. The team concentrated efforts on a retrospective study consisting of more than 1,300 women (54% Caucasian, 38% Hispanic, and other/missing 8%; average age 28 years). The women in the study sought help at the Emergency Department following a miscarriage (up to 20-weeks gestation) between 2007 to 2015. The team examined the risk of miscarriage during a three- or seven-day window following a spike in the concentration of three common air pollutants: small particulate matter (PM 2.5), nitrogen dioxide and ozone. The study excluded women who lived outside Utah. Scientists note the results suggest there could be an increased risk for an individual.
Their research only captured women who sought help at an emergency department at one hospital in the region. It does not account for women who may have sought outpatient care through their obstetric or primary care providers. The team found a slight increased risk in miscarriage for women exposed to elevated levels of nitrogen dioxide (NO2; 16% for 10 ppb increase during the seven-day window). Although small particulate matter does track with nitrogen dioxide, these results did not significantly associate with an increased risk of miscarriage. The Wasatch Front experiences short-periods of poor air quality, primarily during the winter months, when inversions trap pollutants close to the ground (for the 7-day window: PM2.5 min= 0.3ug/m3; PM2.5 max= 73.0ug/m3; O3 min= 4ppb; O3 max= 80ppb; NO2 min= 0.5ppb; NO2 max= 65ppb). The researchers tracked air quality by zip code, establishing six designated air basins within the Wasatch Front. They compared air quality in each basin to their patients’ outcomes. The team conducted a case cross-over study that estimated a woman’s risk of miscarriage multiple times in a month where air pollution exposure varied. This approach removed other risk factors from the study, like maternal age.
Dr. Matthew Fuller, MD, assistant professor of Surgery and senior author on the paper, explains and comments: “We are really only seeing the most severe cases during a small window of time. These results are not the whole picture. Not being from Salt Lake originally, I noticed a pattern in the relation to air quality and pregnancy loss. I knew this was an understudied question so we decided to dig deeper. While we live in a pretty unique geographic area, the problems we face when it comes to air pollution are not unique. As the planet warms and population booms, air pollution is going to become a bigger problem not only in the developing world but across the United States. I recommend women speak with their doctor about any health concerns. Women can manage the risk by using a N95 particulate respirator face mask to filter out pollutants or avoid outdoor physical activity on poor air quality days. Women can also use filters to lower indoor pollution and, if possible, time conception to avoid seasonal episodes of poor air quality”.
The scientists were unable to ascertain the age of the fetus at the time of the miscarriage and were unable pinpoint a critical period when the fetus may be most vulnerable to pollutants. No mechanisms was investigated how NO2 or particulate might affect fertility or miscarriage in the study. However, from a previous review of the literature, scientists were able to prove that exposure to particulate matter (PM) and nitrogen dioxide (NO2) showed consistent inverse associations with mitochondrial DNA (mtDNA) content, particularly in the third trimester of pregnancy. Oxidative stress and inflammatory events could play a role, since C-reactive proteins (CRPs) and oxidative stress markers increased, whereas telomere length decreased with increasing air pollution exposure. Most studies provided insufficient evidence for characterizing a critical exposure window. The only exception are those on DNA adducts with carcinogen polycyclic hydrocarbons (PAHs) and mtDNA content, which represent direct dosable damage. Further studies on the topic have been published by other groups.
Last year, a joint team form the Taijin Normal University and the Chinese Research Academy of Environmental Sciences at Beijing, found that maternal exposures to ambient PM2.5 particulate during a critical time window following conception are associated with early pregnancy loss, with the second week after conception possibly being the exposure window of most vulnerability. Then a team from Schools of Public Health in Atlanta and Boston used data from the Nurses’ Health Study II, who contributed a total of 35 025 pregnancies between 1990 and 2008. In the 19 years follow-up, almost 6600 miscarriage events were reported, being positive associations between exposure to all size fractions of PM exposure (2,5, 5 or 10) and risk of miscarriage, especially for those women living closer to a major raodway. Though other studies will surely be performed, these data already suffice to state that air pollution, among the other risk factors, must be taken in account for the overall incidence of spontaneous abortions.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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