LONDON, Nov. 17 (UPI) -- It's long been known slightly more boys are born because fewer survive, but British researchers have pinpointed several reasons why boys are the weaker sex.
Professor Joy Lawn, director of the London School of Hygiene & Tropical Medicine's Centre for Maternal, Adolescent, Reproductive & Child Health, says while baby boys have a higher likelihood of infections, jaundice, birth complications and congenital conditions, their greatest risk is preterm 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," Lawn said in a statement. "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 preterm 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 preterm births."
However, after the first month of life, in some societies where girls receive less nutrition and medical care, the girls are more likely to die than boys, despite this biological survival advantage for girls, Lawn said.
Of the 15.1 million babies born too soon every year, about 1 million die due to prematurity, accounting for one-third of the world's 2.9 million newborn deaths, a huge impact for families, societies and economies in both high and low-income countries, the study said.
In developed nations, more than 80 percent of infants born under 37 weeks survive and thrive, but risk of death and disability is greatest for those born at fewer than 28 weeks.
However, infants who survive preterm birth face lifelong physical and intellectual disabilities and even babies born just a few days early are more likely to be re-hospitalized and have learning and behavioral challenges, the study said.
The study, published in the journal Pediatric Research, found boys are 14 percent more likely to be born preterm than girls. Disabilities that can result from preterm birth range from learning problems and blindness to deafness and motor problems, including cerebral palsy, Lawn said.