Study Examines Toll of Preterm Birth
Monday, October 5, 2009
Around the world, about one in 10 babies are born prematurely each year, and more than one-quarter of the deaths that occur in the month after birth are the consequence of preterm birth.
Those are among the findings of a new study of the burden of preterm birth by the World Health Organization and the March of Dimes.
The global health community is focusing renewed attention on maternal-child illness and mortality. The new study, which will be followed by a country-by-country assessment next year, looks at the specific role of prematurity in the problems of newborns.
"These are striking data that really surprised us," said Christopher Howson, a March of Dimes researcher who helped prepare the report.
About 12.9 million babies are born too soon each year, representing 9.6 percent of births. Of 4 million deaths that occur soon after birth, 28 percent are attributable to prematurity.
Some of the information provided by WHO is only for women pregnant with one baby. Women carrying multiples have a much greater risk of delivering early.
"We know the figures in this report are conservative," Howson said. "I think we can say very clearly that the situation on the ground is more dire than this suggests."
Preterm birth is defined as birth before 37 weeks of gestation. A typical pregnancy lasts 40 weeks. Rates and causes of preterm birth vary widely by region.
Africa has the highest rate (11.9 percent), followed by North America (10.6 percent) and Asia (9.1 percent). Latin America and the Caribbean are midrange (8.1 percent), and Australia and New Zealand (6.4 percent) and Europe (6.2 percent) are the lowest.
Relatively little is known about the causes of prematurity in the developing world. However, malnutrition, coexisting illnesses such as malaria and anemia and inadequate prenatal care are likely factors, Howson said.
Other variables are probably at play in the United States, where the rate of preterm birth has increased 36 percent in the last quarter-century. (It stands at 12.7 percent; the North American rate is brought down by Canada's 8.2 percent rate).
The increase in the number of older women having babies and reproductive techniques that make multiples more likely are probably contributing to the trend. Black women also have a 50 percent higher rate of preterm delivery than whites.
Most of the increase in preterm birth in the United States is from deliveries between 34 and 36 weeks of gestation, known as "late preterm" birth. Once thought to carry little risk, even that lesser degree of prematurity is known to be hazardous.
In a study published last year, the University of Texas Southwestern Medical Center in Dallas examined 18 years of single-birth records. Late preterm babies were 9 percent of all deliveries and 76 percent of all premature births. Mortality was low, but more than twice that of full-term babies. The preemies also were more likely to need breathing assistance, be jaundiced and develop infections.
Eighty percent of the late preterm births were the result of early labor or rupture of membranes -- problems that are usually without obvious cause.
The report did not outline strategies for reducing preterm births globally, but a more detailed study due in 2010 is expected to do so.