Fifteen million babies, or one in 10 around the world are born premature every year, and 1.1 million of those infants die, according to a UN-sponsored report.
Premature birth is the leading cause of death for newborn infants and is on the rise globally, said the report led by the March of Dimes, The Partnership for Maternal, Newborn & Child Health, Save the Children and the World Health Organization.
The study defined preterm birth as occurring before 37 weeks of pregnancy are complete. Typical pregnancies last 38-40 weeks.
What the study found
Southern Asia leads the world with the highest preterm birth rate, with 13.3% of babies born early, followed by Sub-Saharan Africa at 12.3%, it said. Together, Africa and South Asia account for 60% of all preterm births.
The developed world's overall preterm birth rate came in at 8.6%.
Malawi had the highest rate of early births of any of the 184 countries studied, with more than 18%, followed by Congo, Comoros and Zimbabwe.
Pakistan and Indonesia ranked eighth and ninth highest, while the lowest preterm birth rate was in Belarus at under 5%.
When it came to counting numbers of preterm births in the world, rather than birth rates, the highest numbers were in India, China, Nigeria, Pakistan, Indonesia and the United States.
Those countries were the leaders of a group of 15 that accounts for two-thirds of the world's preterm births, the report said.
"There is a dramatic survival gap for premature babies depending on where they are born," it added, noting that more than 90% of babies born before 28 weeks in low-income countries die within the first few days of life.
In high income countries, fewer than 10% of these babies die, it said.
What causes preterm birth
The causes of preterm birth are often unknown, but there may be links to genetic influences, high blood pressure, diabetes, infections or chronic conditions.
Teen pregnancy, short time gaps between births, being underweight or overweight prior to conception and substance or alcohol abuse are also risk factors. - (AFP, May 2012)
Smoking ban leads to fewer preterm births