Almost twice as many infant deaths than previously estimated, are because babies are born prematurely.

According to a new analysis by researchers at the U.S. Centers for Disease Control and Prevention in 2002 preterm birth, which is birth at less than 37 completed weeks gestation, contributed to more than one-third of infant deaths within the first year of life.

Dr. B Callaghan, the research team leader, reviewed 27,970 infants who died in 2002 and found 17%, or 4,600 of them, had pre-term birth as the reason for their death.

But there were 5,000 other deaths where the babies died of conditions very closely linked to pre-term births, such as respiratory distress syndrome, brain hemorrhage and premature rupture of membranes.

Dr. Callaghan says the figure should have been 9,600 of the deaths (34%) were due to pre-term births and not just 4,600.

The report found that the U.S. infant mortality rate has been in decline since 1995 except between 2001 and 2002, when the rate increased for the first time since 1958.

Joann Petrini, Ph.D., director of the March of Dimes Perinatal Data Center says experts have always known that babies born too early face many challenges and even death, but this new research confirms the urgent role preventing preterm birth can play in improving infant mortality in the United States.

In 2002, the National Center for Health Statistics listed short gestation/low birth weight as the cause of 17 percent of infant deaths.

However, the CDC researchers also found that two-thirds of the infants who died in 2002 were born prematurely and this difference they say suggests that premature birth plays a greater role in infant death than the official reporting system indicates.

The researchers reviewed the causes of infant death and combined conditions, such as respiratory distress syndrome, which frequently occur in premature babies.

These criteria saw a doubling in the percentage of infant deaths caused by premature birth to 34.3 percent and more than 95 percent of those deaths were of infants who were born at less than 32 weeks gestation, the definition of infants who are “very preterm.”

According to official reporting systems birth defects are the leading cause of infant death, followed by prematurity, but this new classification method indicates that premature birth is the most frequent cause of infant death.

The revelation is significant as 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 challenges of cerebral palsy, mental retardation, chronic lung disease, vision and hearing loss, as well as other developmental problems.

The researchers say that rather than excluding pre-term birth from the reason of death in many illnesses, it should be included.

Healthcare professionals who are provided with accurate statistics are then better equipped to advise pregnant women on the health measures to take to reduce their chances of having a premature birth.

The report is published in the current issue of Pediatrics.