Boys are 14% more likely to be born prematurely than girls, according to a new study.
Professor Joy Lawn, a neonatologist and epidemiologist at the London School of Hygiene and Tropical Medicine (LSHTM) said: "Baby boys have a higher likelihood of infections, jaundice, birth complications, and congenital conditions but the biggest risk for baby boys is due to pre-term birth.
"For two babies born at the same degree of prematurity, a boy will have a higher risk of death and disability compared to a girl.
"Even in the womb, girls mature more rapidly than boys, which provides an advantage because the lungs and other organs are more developed.
"One partial explanation for more pre-term births among boys is that women pregnant with a boy are more likely to have placental problems, pre-eclampsia, and high blood pressure - all associated with pre-term births."
Professor Lawn said boys had a biological predisposition to being born early. "In the UK, an extra 6,000 boys or so are born pre-term each year," she said.
The studies found higher rates of disability in boys across a range of health problems, including cerebral palsy, blindness and visual impairment.
"If you are born premature, even that little difference in maturity between girls and boys can make a big difference – particularly in breathing complications for boys," said Professor Lawn.
Professor Lawn's research was a global study on premature birth, which she said was a major problem around the world.