Preterm related deaths accounted for more than 10,000 of the nearly 28,000 infant deaths in 2004, according to the NCHS. Birth defects remain the leading cause of infant death, followed by prematurity, according to official reporting systems. But, using this new classification, premature birth would be the most frequent cause of infant death. The traditional methods cannot accurately gauge the true impact of preterm birth on the infant mortality rate, the NCHS said.

Although the national infant mortality rate is the lowest it's been since the U.S. started collecting data a century ago, there's been little change recently – 6.78 deaths for every 1,000 live births in 2004 compared to 6.89 in 2000, the National Center for Health Statistics report found.

The report, "Infant Mortality Statistics from the 2004 Period Linked Birth/Infant Death Data Set" includes a new analysis tracking preterm birth-related infant deaths. The analysis, first published in the October 2006 edition of Pediatrics, found preterm birth contributes to nearly twice as many infant deaths within the first year of life than previously estimated.

"We have long known babies born too soon face many developmental challenges – even death," said Joann Petrini, Ph.D., director of the March of Dimes Perinatal Data Center. "This closer look at preterm birth gives us a better understanding of the impact of prematurity on infant survival and provides insights into the factors that have contributed to the lack of improvement in the U.S. infant mortality rate."

The new method reviews all causes of infant death and combines conditions, such as respiratory distress syndrome, which frequently occur in premature babies. The analysis published in October 2006 looked at only the top 20 leading causes of infant death.

More than a half million babies are born too soon each year and the preterm birth rate has increased more than 30 percent since 1981. Babies who do survive face risks of lifelong health and developmental challenges.

Source: March of Dimes.