Middle-income countries are missing out on a lesson the U.S. learned the hard way several decades ago, that giving these tiny babies too much oxygen can trigger a potentially blinding condition called retinopathy of prematurity.
"Disability is not something that's inevitable. It's preventable," she said, calling for improved quality of care including eye checks to prevent or reduce vision loss.
The March of Dimes reported this month that 11.5 percent of U.S. births now are preterm. That rate is inching down, thanks mostly to fewer babies being born just a few weeks early as standards for elective deliveries have tightened, but it still is higher than in similar countries.
For the public, the gender difference may be the most surprising finding of Friday's report, although Dr. Edward McCabe of the March of Dimes says pediatric specialists have long noticed that baby boys start out a bit more vulnerable.
"People are curious about it. We'd like to understand why this occurs," McCabe said.
One possible reason: Mothers have a higher risk of certain pregnancy complications - high blood pressure and placenta abnormalities - when carrying boys, Lawn said.
And if a boy preemie and a girl preemie are born at the same gestational age, the boy will be at higher risk of death or disability, she said. But Friday's report concluded there is too little information to quantify how big that risk is.
"Girls walk sooner than boys. They talk sooner than boys. They develop more quickly. That's also true in utero," Lawn said. For a preterm baby, "the difference of a few days maturity between a boy and a girl can mean the difference between major lung complications or not."
It's not just a prematurity issue. The report found that full-term boys also are more likely than girls to experience other newborn health problems including birth complications.
Other findings from the studies, funded by the Bill & Melinda Gates Foundation and published in the journal Pediatric Research:
- In high-income countries - the U.S., Canada, Australia and most of Europe - more than 80 percent of preemies both survive and thrive, although babies born even a little premature are more likely than full-term babies to be rehospitalized or have learning and behavioral challenges.
- In low-income countries, preterm babies are 10 times as likely to die as those in high-income countries, and death is more common than surviving with a serious disability.
- Aside from preterm birth, other leading causes of death and disability among newborns include birth complications that block breathing; severe jaundice and infections.