Boys are slightly more
likely to be born premature than girls, and they tend to fare worse, says a new
report on the health of the world's newborns.
"It's a pattern that
happens all over the world," said Dr Joy Lawn of the London School of
Hygiene & Tropical Medicine, who led the team of researchers.
The gender difference isn't
large: About 55% of preterm births in 2010 were male, the report found. It's
not clear exactly why it happens.
The finding comes from a
series of international studies 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 another million die of conditions for which prematurity is
an added risk, the researchers calculated.
Where and when
Friday'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%
of survivors have two of the most burdensome disabilities:
neurologic-developmental impairment ranging from learning disabilities to
cerebral palsy, and vision loss.
But the biggest risk is to
the youngest preemies, those born before 28 weeks gestation. Worldwide, 52% of
them are estimated to have some degree of neuro-developmental impairment, the
Moreover, the risk of
impairment in middle-income countries is double that of wealthy countries like
For example, China is
saving more preemies' lives but at the cost of their vision, Lawn said.
Middle-income countries are
missing out on a lesson the US 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 gender difference
The March of Dimes reported
this month that 11.5% of US 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
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 paediatric specialists have long
noticed that baby boys start out a bit more vulnerable.
"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."
Newborn health problems
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 Paediatric Research:- In high-income countries –
the US, Canada, Australia and most of Europe – more than 80% of preemies both
survive and thrive, although babies born even a little premature are more
likely than full-term babies to be rehospitalised or have learning and behavioural
- 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.
- Besides preterm birth,
other leading causes of death and disability among newborns include birth
complications that block breathing; severe jaundice and infections.