Preventing early births rather than increasing birth weights may be the key to having more babies born healthy and surviving, a study finds.
The infant mortality study comparing figures from the United States and Norway contradicts previous research suggesting birth weight is crucial, the researchers said in Wednesday’s issue of The Journal of the American Medical Association.
Low birth weight - defined as less than 5.5 pounds - may result from early birth, but only about 40 percent of low birth weight babies are born early, said lead author Dr. Allen Wilcox, chief of epidemiology at the National Institute of Environmental Health Sciences.
Those who think the United States can lower its infant mortality, currently worse than 21 other industrial countries, have stressed efforts to bolster birth weight. These include programs to get pregnant women eating right and not smoking.
These programs may be helpful, scientists say, but more study is needed about why babies are born early.
“For every study trying to figure out the causes of preterm delivery, there have been 10 trying to figure out the causes of low birth weight,” said Wilcox, also an adjunct professor at the University of North Carolina at Chapel Hill.
Wilcox’s team analyzed 7.5 million birth records from the United States and 105,000 from Norway from 1986-87, the most recent two-year period available.
Infant mortality, defined as the death of the fetus in the womb or of the infant during the first four weeks, was 10 percent lower in Norway. That country also had fewer preterm babies - 2.1 percent of its total compared with 2.9 percent of U.S. babies.
“If we just look at term babies, they have the same infant mortality in the United States as in Norway,” even though the U.S. babies have lower average weight, Wilcox said Monday from Research Triangle Park, N.C.
What’s more, the average U.S. baby still would be smaller than the average Norwegian baby even if all U.S. babies had the weight of full-term U.S. babies, Wilcox said. That suggests birth weight is simply a national trait, not a survival advantage, he said.
Representatives of the American Academy of Pediatrics and of the federal Centers for Disease Control and Prevention agreed.