Pregnant women living in neighborhoods with lots of greenery are more likely to give birth at full term, and their babies are born with higher weights, according to a new study.

The study was conducted by researchers from Oregon State University and the University of British Columbia.

"This was a surprise," said Perry Hystad, an environmental epidemiologist in the College of Public Health and Human Sciences at Oregon State and lead author of the study, in a press statement. "We expected the association between greenness and birth outcomes to disappear once we accounted for other environmental exposures such as air pollution and noise. The research really suggests that greenness affects birth outcomes in other ways, such as psychologically or socially."

Researchers analyzed data of more than 64,000 births. They found that extreme pre-term births were 20 percent lower and moderate pre-term births were 13 percent lower for infants whose mothers lived in greener neighborhoods. Researchers also noted that fewer infants from greener neighborhoods were considered small for their gestational age.

"From a medical standpoint, those are small changes in birth weight, but across a large population, those are substantial differences that would have a significant impact on the health of infants in a community," Hystad said.

Researchers were not able to determine the exact mechanism behind this phenomenon and suggest further studies to be carried out on this topic. One speculation is that green space provides more social opportunities and enhances a person's sense of belonging in the community. Researchers also speculate that more greenery has a psychological effect which reduces stress and depression, leading to better birth outcomes.

"We know a lot about the negative influences such as living closer to major roads, but demonstrating that a design choice can have benefits is really uplifting," said the study authors. "With the high cost of healthcare, modifying urban design features such as increasing green space may turn out to be extremely cost-effective strategies to prevent disease, while at the same time also providing ecological benefits."

Findings of the study were published recently in the journal Environmental Health Perspectives. The research was supported by a grant from Health Canada.