The U.S. infant mortality rate rose in 2002, the first such increase since 1958, researchers at the Centers for Disease Control and Prevention reported.
The increase, from 6.8 infant deaths/1,000 live births in 2001 to 7/1,000 live births in 2002, was primarily driven by an increase in the number of babies weighing less than 750 g at birth.
Between 2001 and 2002, the number of infants weighing less than 500 g increased by 5.1% (330 births), and the number weighing from 500 to 750 g increased by 1.9% (209 births). These changes accounted for 81% of the total increase in infant mortality between the 2 years.
Although the absolute rise in infant deaths was not very large, it is of concern, said Joyce A. Martin, one of the study's authors and a CDC epidemiologist.
“Any increase is a concern, especially when the rate had been going down steadily for 40 years,” she said in an interview.
Maternal race was not a significant factor in the increase, but age was, the researchers said. Most of the increase (82%) occurred among women aged 20–34 years, a period that is generally not considered at high risk for poor birth outcomes.
The researchers said that several factors appear to have contributed to the increase. Multiple gestations were one, but accounted for only 25% of the increase.
Maternal illness might have had an impact. In 2002, there was a slight increase in maternal anemia, diabetes, and chronic hypertension. It's difficult to assess the actual impact of these changes on the infant mortality rate. These conditions are also associated with an increased risk of medical intervention resulting in early delivery.
In 2002, 48% of very preterm births and 38% of moderate preterm births were born by cesarean—increases of more than one-third since 1990. In 2002, among birth of infants weighing 500–750 g, 65% were cesarean deliveries. The authors couldn't determine whether these increases reflected actual changes in the medical management of pregnancy, or were due to prematurity related to maternal illness.
The increased incidence of assisted reproductive technology also may have influenced the mortality rate. Although the vital records used in the study didn't contain assisted reproductive technology information, some links can be drawn from societal trends and the results of other studies, Ms. Martin said. “We know from some recent studies that even singletons conceived through ART have an increased risk of low birth weight, prematurity, and neonatal mortality,” she said. “This may have had an impact, although we can't tie the increase in mortality to ART.”
To see a copy of the report go to www.cdc.gov/nchs