State-wide study links well-connected, closely distributed greenspace with lower risk of preterm birthA substantial body of research has linked neighborhood greenspace to improved birth outcomes, including healthier birth weights and a decreased risk of preterm birth. However, the influence of greenspace morphology—the physical characteristics and spatial organization of greenspace—on birth outcomes remains poorly understood. This population-based state-wide study is the first of its kind to examine whether residential greenspace morphology, including greenspace percentage, shape of the land, connectedness between greenspace areas, aggregation, proximity to green space, and fragmentation, is related to preterm birth. The study analyzed birth record data from over two million pregnant mothers and infants to explore these potential associations. Additionally, because disparities in preterm birth rates are widely documented, the study examined whether the relationship between residential greenspace morphology and preterm birth differs based on race, ethnicity, urbanicity, and neighborhood poverty level.
The study used birth record data on 2,040,007 live births in Georgia, US, between 2001 and 2016. Only singleton pregnancies with gestational ages from 27 to 42 weeks were included in the study. Births with missing data, such as maternal residence and sociodemographic information, were excluded. The sample included 164,369 (8.9%) preterm births, which were defined as a live birth occurring at less than 37 weeks of gestation. Greenspace morphology was evaluated using 30-meter resolution National Land Cover Database imagery. Greenspace was defined to encompass grasslands, shrublands, forests, and developed open spaces characterized by vegetation/grass (such as parks, golf courses, and urban vegetation). Greenspace morphology was quantified for 1,953 census tracts across the state. Half-mile buffers (approximately a 10-minute walking distance) were extended around the perimeter of each census tract to account for real-world greenspace exposure. Six landscape metrics were calculated for each buffered tract: fragmentation (separated greenspace areas), connectedness (greenspaces with connections, such as trails, linking them), aggregation (adjoined green spaces), distantness (distance between neighboring green spaces), shape complexity (green space shapes that have many sides and angles vs, for example, a solid circle or square), and the percentage of land area considered greenspace. Tract-level greenspace data were linked to each mother based on their residential location. Statistical analyses examined the relationships between greenspace morphology metrics and preterm birth. The analyses controlled for individual-level maternal factors that have been linked to adverse birth outcomes, including maternal age and education level, race, ethnicity, marital status, and tobacco use. A secondary analysis adjusted for census tract-level poverty rates. Potential shifts in the relationships between greenspace morphology and preterm birth were also examined across subpopulations, including maternal race (black vs. non-black), maternal ethnicity (Hispanic vs. non-Hispanic), maternal education level, pregnancies residing in high-poverty census tracts, and pregnancies residing in high urbanicity counties.
A higher percentage of neighborhood green space was linked to a reduced risk of preterm birth. This relationship was more pronounced among black mothers, especially within high-urbanicity counties with greater economic disadvantage. Protective relationships were consistently detected between higher greenspace percentage, aggregation, shape complexity, and connectedness, and lower distantness and fragmentation, and a reduced risk of preterm birth. Again, these relationships were stronger among black mothers, as well as mothers with education beyond high school and mothers in high-urbanicity areas. The relationship between greenspace morphology and preterm birth was also significant among both Hispanic and non-Hispanic groups. When analysis accounted for census tract poverty level, the relationships between greenspace morphology and preterm birth outcomes weakened, except for fragmentation, which remained significantly linked with higher risks of preterm birth across the entire population. However, findings varied when subpopulations were examined. For black mothers, the relationship between greenspace morphology and preterm birth remained significant. Among black mothers specifically, higher greenspace percentage and aggregation were linked to a lower risk of preterm birth, and higher fragmentation was linked to an increased risk, even after controlling for poverty indicators. Additionally, among the Hispanic mother group, higher greenspace percentage and connectedness remained significantly linked to a reduced risk of preterm birth when poverty level was accounted for. For higher poverty census tracts, higher greenspace percentage and aggregation were linked to a lower risk of preterm birth, while higher greenspace fragmentation was linked to a higher risk of preterm birth. Finally, when greenspace percentage was categorized into low, medium, and high levels, the relationship between greenspace morphology and preterm birth risk was most pronounced in census tracts with a medium level of greenspace percentage. The authors suggest that in areas with a lower percentage of greenspace, green space is too sparse to offer much morphological variation, which limits its effectiveness; areas with a high percentage of greenspace may include large, well-connected parks of sufficient cohesion to potentially overshadow the importance of particular morphological traits.
This first investigation into the relationship between greenspace morphology and preterm birth outcomes contributes to a growing body of evidence documenting the public health benefits of greenspace and, specifically, the importance of greenspace spatial morphology. Overall findings “suggest that pregnant women residing in urban areas characterized by a higher greenspace percentage, more aggregated and connected greenspaces, spatially close distribution, and complex shapes are associated with a reduced risk of preterm birth.” Notably, these protective effects were found to be most pronounced among black women, pregnant mothers living in high-poverty neighborhoods, and in urban areas with a medium level of greenspace percentage. Results of this study align with related research showing that greenspace morphology is linked to numerous health outcomes. The links between greenspace morphology and preterm birth may be explained by reduced air pollution and cooler temperatures, which can impact birth outcomes. Greenspace morphology might also influence how pregnant women utilize greenspace. For instance, well-connected parks might encourage increased physical activity, improving the physical and mental health of pregnant women. The researchers conclude that “investing in urban nature to enhance spatial closeness, connectedness, aggregation, cohesion, and shape complexity, and filling in spatial gaps between greenspaces at the neighborhood scale might lead to improved birth outcomes.”
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