More infant deaths tied to premature birth

ATLANTA — Scientists now say a third of infant deaths are due to premature births, a much larger percentage than previously thought.

In the past, "preterm birth" has been the listed cause of death in fewer than 20 percent of newborn fatalities. But that number should be 34 percent or more, said researchers at the U.S. Centers for Disease Control and Prevention.

That's because at least a dozen causes of newborn death are actually problems that go hand in hand with premature births, such as respiratory distress syndrome caused by underdeveloped lungs.

"This brings preterm birth, as a cause of death, to the kind of level that we think it deserves," said the CDC's Dr. Bill Callaghan, the lead author of a study appearing today in the journal Pediatrics.

"What this says is that we need to focus a lot more effort on prevention and the study of what leads to prematurity," said Dr. Gabriel Escobar of the Kaiser Permanente Division of Research in Oakland, Calif., who was not associated with the study.

"In the United States, the death rate in [full] term babies without congenital anomalies is approaching zero," he said. "If we want to save babies, we have to focus on preemies."

And that means focusing more on the mothers, Callaghan said. "We are approaching the limits of technology to keep the infants alive," he said. "If anything is going to be done to make a major movement, it's the prevention of preterm births."

"Preterm birth" generally describes infants who are born before 37 weeks gestation. A full-term pregnancy lasts 38 to 42 weeks.

According to a National Academy of Sciences report issued this summer, 1 in 8 infants born in 2004 — the most recent year for which figures are available — was premature, a 30 percent increase over the rate in 1980. The reason for the increase is unknown.

The rate of prematurity is lowest in whites, slightly higher is Hispanics and highest in blacks, said Joann Petrini, director of the March of Dimes Perinatal Data Center. "But the rates are increasing for everyone," she said.

The U.S. mortality rate, which declined for several decades, stabilized at about 6.8 deaths per 1,000 births in 1999, a rate substantially higher than in other industrialized countries. Those preterm children who survive often suffer from severe physical and behavioral defects, at a cost of about $26 billion per year.

Callaghan and his colleagues studied 27,970 births in 2002 for which both birth and death certificates were available and linked.

More than 4,600 of those — or 17 percent — were attributed solely to preterm birth. But the researchers also grouped in about 5,000 other deaths that were attributed to preterm-related conditions including respiratory distress syndrome, brain hemorrhage and maternal complications such as premature rupture of membranes.

In that counting, nearly 9,600 births — or 34 percent — could be classified as preterm, Callaghan said. The researchers think that figure is conservative and likely underestimates the true picture.

Escobar said the findings show that more research needs to be conducted on the causes of prematurity and the ways it can be averted.

"Every day that you keep a baby in that womb makes a difference," he said.