Infant Mortality

Leading Causes of Infant Mortality

Until the 1990s, the most common cause of infant mortality worldwide has been dehydration from diarrhea. The successful distribution and use of oral rehydration solution (a mixture of salt, sugar, and water) has decreased the incidence of infant death by dehydration. In the 1990s, pneumonia replaced [Page 563]dehydration as the most common cause of infant mortality worldwide. In the United States, congenital malformations and chromosomal abnormalities accounted for the highest number of infant deaths in 2003. Preterm delivery (delivery before the end of the 37th week of pregnancy) and low birthweight accounted for the next-highest-rated cause that year, followed by sudden infant death syndrome (SIDS).

Congenital malformations are physical defects present in babies at birth, regardless of whether the defect is caused by a genetic factor or by prenatal effects not related to genetics. In a malformation, the development of the fetal structure is arrested, delayed, or misdirected early in embryonic life and the effect is permanent. These defects can occur for many reasons, including inherited (genetic) conditions; toxic exposure of the fetus (for example, to alcohol); and birth injury. All parents are at risk of having a baby with a birth defect, regardless of age, race, income, or residence.

Very little is known about the causes of low birth-weight and preterm birth, despite extensive research. Known risk factors include: cigarette smoking during pregnancy, low maternal weight gain and low prepregnancy weight, prior preterm birth, and low prepregnancy weight. However, these account for less than one-quarter of preterm births.

SIDS is the sudden death of an infant less than 1 year of age that cannot be explained by information collected during a thorough forensic investigation. Although the overall rate of SIDS in the United States has declined by more than 50 percent since 1990, rates have declined less among African American and American Indian/Alaska Native infants. SIDS is the leading cause of death among postneonatal infants.

Prevalence of Infant Mortality

Globally, the infant mortality rate has declined over the last several decades, from 126 in 1960 to 57 in 2001. In the United States, infant mortality has steadily decreased over the last several decades (except for a slight increase in 2002). In 1960, the U.S. rate was 26; in 1982, 11.5; in 1992, 8.5; and in 2002, 7, up 0.2 percent from 2001. In 2008, the rate was estimated at 6.3. However, despite these decreases, the United States currently ranks 41st of 222 nations for which reliable statistics are available (2008 estimate). The highest infant mortality rate globally is in Angola (182.4); Sierra Leone is the next highest at 156.5, followed by Afghanistan's rate of 154.7. The lowest rate is Singapore's, at 2.3. The United States' low ranking is due in large part to health disparities among racial and ethnic groups.

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