An increasing number of unexplained premature births threatens recent progress toward reducing infant mortality, which has fallen to a record low, federal health officials said Thursday.
The U.S. Centers for Disease Control and Prevention (CDC) said infant mortality fell to 8.4 deaths per 1,000 live-born infants in 1993, the lowest rate ever recorded. The figure was a 1.8 percent decrease from the 1992 rate of 8.5 per 1,000.The biggest causes of infant death are birth defects, sudden infant death syndrome, disorders related to premature birth and respiratory distress, the CDC said. These accounted for 54 percent of all U.S. infant deaths in 1993.
Deaths attributable to short gestation (premature birth) or low birth weight more than doubled for both white and black infants between 1985 and 1991, increasing from 5.6 percent to 11.5 percent of first-year infant deaths.
"This seems to be a group of infants who are premature. The reason why they're premature isn't understood. They're sort of mystery babies," said Paula Gardner, a survey statistician in the CDC's National Center for Health Statistics.
The CDC said there was a 7.2 percent increase in infants born with low birth weight from 1992 to 1993.
"While the increase in the number of multiple births explains some of that, it doesn't explain why it's already so high and is staying high," Gardner said.
Infant deaths from respiratory stress syndrome and infection have fallen, she said. Deaths from birth defects have also fallen, particularly among blacks.
Black infants were 2.4 times as likely to die before their first birthday, the CDC said. The 1993 mortality rate for black infants was 16.5 percent per 1,000, a 1.9 percent decrease from 1992. For white infants, the rate was 6.8 per 1,000, a 1.4 percent decline.
In 1991, the United States ranked 24th in infant mortality among countries with population over a million.
The U.S. rate in 1991 was 8.9 deaths per 100,000 live births. Japan had the lowest rate of 4.43, followed by Singapore with 5.44.