Researchers at the March of Dimes Prematurity Research Center (PRC) at the University of Pennsylvania (UPenn) have found that pregnant individuals who lived in urban neighborhoods with fewer trees were more than twice as likely to develop hypertensive disorders compared to pregnant people who lived around more trees.
The research, published recently in the American Journal of Perinatology, was led by UPenn PRC scientist and neonatologist Dr. Heather Burris and Dr. Max Jordan Nguemeni, an internal medicine resident at Brigham and Women’s Hospital in Boston, Mass. It was also co-authored by UPenn Associate Professor of Emergency Medicine Dr. Eugenia South, a national expert on the impact of green spaces on health equity, with a focus on using green spaces to curb gun violence.
Drs. Burris and Nguemeni and their team found that study participants living in Philadelphia whose homes were within 100 meters of an area with less than 10 percent tree cover had more than twice the odds of developing Hypertensive Disorders of Pregnancy (HDP) compared to participants whose homes were within 100 meters of a green area with more than 30 per cent tree canopy. This was true even when controlling for the Neighborhood Deprivation Index (NDI), which is calculated using factors like neighborhood income and education level.
Chief among HDP is preeclampsia, the most common and serious high blood pressure disorder of pregnancy, which disproportionally affects non-Hispanic Black pregnant people. Some recent research has led scholars and scientists to assert that lived experience – by way of overt and/or structural racism — plays a significant role in the development of the disease for non-Hispanic Black individuals.
Whether tree canopy comes in the form of parks, playgrounds, tree lined streets, forested areas or just trees, living near green spaces has long been thought to be beneficial to health. Some ways trees and green spaces are thought to help are by improving respiratory symptoms due to the trapping of air pollutants and providing temperature-lowering shade, and encouraging exercise through availability of nature paths, which may improve heart health and provide other health benefits, including improved mental health.
Now, the research by Drs. Burris and Nguemeni shows green spaces may help lower the risk of gestational hypertensive disorders like preeclampsia, the second leading cause of maternal death globally.
“Our findings suggest that investing in neighborhood greenspace may be a strategy to reduce HDP and improve perinatal health equity,” Dr. Burris said. “While more research is needed to determine exactly how tree canopy cover decreases the chance of preeclampsia and other gestational blood pressure disorders, this work presents a natural intervention that could may dramatically decrease the risk of one of the worst pregnancy outcomes.”
The majority of the 1,225 participants in the study by Drs. Burris and Nguemeni, over 70 percent, were non-Hispanic Black pregnant individuals who received prenatal care in Philadelphia and participated in Dr. Michal Elovitz’s National Institutes of Health (NIH)-funded Motherhood & Microbiome cohort.
Those with more tree cover around their homes were less likely to develop HDP than those living in ‘gray’ areas with fewer trees and more concrete surfaces like roads, buildings and parking lots.
Indeed, high neighborhood greenness, or a significant percent of tree shade in a particular area, has often been associated with higher income households, whereas low green canopy cover is often found in low-income neighborhoods, more often populated by communities of color.
According to a 2021 piece in The New York Times, age-old discriminatory federal policies, including ‘redlining,’ led to many urban areas throughout the U.S., including in Philadelphia, receiving limited economic growth opportunities due to the area’s racial composition. As a result, many of these areas don’t receive investments in establishing and maintaining green spaces.
For example, the Times found that one part of Chestnut Hill, a higher-income area of Philadelphia, has a median household income of about $133,000, and contains more than 60 per cent tree canopy cover. Compare that with the nearby area of Nicetown-Tioga, where one pocket of homes has a median household income of about $37,000, and contains just 6 per cent tree canopy cover. It also results in average temperatures more than 10 degrees higher than the Chestnut Hill community.
The Times also found that communities that are predominantly white have trees covering over 1/3 of surfaces; in communities of color, that figure drops to 1/5.
Because the study participants in the study by Drs. Burris and Nguemeni lived in different neighborhoods with varied household incomes, her team had to apply a statistical tool to check whether the trees themselves were specifically associated with health benefits or whether the health benefits were a result of higher income and education, which allowed study participants to live in greener neighborhoods.
“In other words, we were able to examine whether benefits were coming from the trees independent of other factors that could result in living in a place with more trees,” said Dr. Nguemeni.
After controlling for Neighborhood Deprivation Index (NDI) which included factors like wealth, income, education, occupation and housing conditions, the UPenn PRC found that trees were still associated with HPD even after socioeconomic differences were accounted for.
The work of Drs. Burris and Nguemeni adds to the scientific community’s understanding of the complex web of interrelated factors influencing the development of preeclampsia in this demographic, and underscores the need to identify the exact biological pathways responsible.
“Although we still have much to learn about preeclampsia and HDP, we are now starting to appreciate that factors beyond individual lifestyle choices may contribute to risk,” Dr. Burris said. “That foundation will, in addition to forming the basis of further studies, allow us to develop relatively straightforward and affordable interventions to help the most vulnerable pregnant people right now.”
In addition to her role at the UPenn PRC, Dr. Burris is also a key member of the scientific team at UPenn’s March of Dimes Research Center for Advancing Maternal Health Equity. The center, which launched in 2023, is working to address poor health outcomes and longstanding racial disparities in pregnancy, birth, and postpartum.