The study looked at nearly 6,000 women and satellite imagery of the tree cover around their homes.
"Tree cover made no difference in the rate of pre-term births, but researchers found a consistent link to the prevalence of infants who were small for their gestational age. For each 10 percent increase in tree coverage within about 50 yards of a home, the rate of undersized newborns decreased by 1.42 per 1000 births. As it stands, about 70 of every 1,000 newborns in Portland are small for gestational age.
'Maybe it sounds a bit daft at first,' says lead author Geoffrey Donovan, a scientist with the U.S. Forest Service's Pacific Northwest Research Station in Portland. But he says it's plausible that having lots of trees nearby counteracts the stress experienced by pregnant women."