Boys are slightly more likely than girls to be born premature, and they tend to fare worse, according to a new report on the health of the world’s newborns.
“This is a double whammy for boys,” said Dr. Joy Lawn of the London School of Hygiene & Tropical Medicine, who led the team of researchers. “It’s a pattern that happens all over the world.”
The gender difference isn’t large: About 55 percent of preterm births in 2010 were male, the report found. Nor is it clear exactly why it happens.
The finding comes from a series of international studies being published today that examine newborn health and prematurity. About 15 million babies worldwide are born too soon, most of them in Africa and parts of Asia where survival is difficult for fragile newborns. Globally, about 1 million babies die as a direct result of preterm birth, and a million more die of conditions for which prematurity is an added risk, the researchers calculated.
Today’s report offers some of the first estimates of how many preemie survivors go on to suffer certain disabilities, and found that where these babies are born, and how early, determines their risk.
Overall, Lawn said about 7 percent of survivors have two of the most burdensome disabilities: vision loss and neurologic-developmental impairment ranging from learning disabilities to cerebral palsy.
But the biggest risk is to the youngest preemies, those born before 28 weeks gestation. Worldwide, 52 percent of them are estimated to have some degree of neurodevelopmental impairment, the report found.
Moreover, the risk of impairment in middle-income countries is double that of wealthy countries like the United States.
For example, China is saving more preemies’ lives but at the cost of their vision, Lawn said.
For the public, the gender difference might be the most surprising finding of today’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 the report concluded there is too little information to quantify how big that risk is.
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.