For more than 20 years, birth defects have been the leading cause of infant mortality.  In 1999, birth defects accounted for 5,480 infant deaths (under 1 year), reflecting a rate of infant mortality due to birth defects of 138.4 per 100,000 live births.  Prematurity/low birthweight (LBW) was the second leading cause of infant mortality (110.5 per 100,000), followed by sudden infant death syndrome (SIDS—66.8), maternal pregnancy complications (35.0), and respiratory distress syndrome (RDS—28.5).  Together, these five causes accounted for more than half of all infant deaths in 1999.