State Reporting of Live Births of Newborns Weighing Less Than 500 Grams: Impact on Neonatal Mortality Rates

Abstract

The National Center for Health Statistics reports that in 1983 65% of all infant deaths in the United States occurred in the neonatal period. Of these reported neonatal deaths, 17% were of infants weighing less than 500 g at birth. There was, however, variation in state-reported incidence of live births of newborns in this weight cohort (0.2 to 2.2 per 1,000 live births). Thé states with the lowest neonatal mortality rate have the lowest incidence of birth weights less than 500 g (ρ = .77). If it is assumed that mortality for this weight category is nearly 100%, there is marked variation (5% to 32%) in the contribution of this weight cohort to a state's total neonatal mortality rate. Contributing to this variation may be definitions of live birth used by states. The World Health Organization defines a live birth as the product of conception showing signs of life "irrespective of the duration of pregnancy" and this definition is used by 33 states. Only one state (Ohio) includes the gestational criteria of "at least 20 weeks" in its definition of live birth. There is evidence to suggest that definitions are not uniformly used within individual states. For example, in 1983, 20 states did not report any live births with weights less than 500 g among their "other" populations of nonwhite, nonblack residents. Half of these states, however, use the World Health Organization definition of live birth. Despite the exclusionary wording in Ohio's definition of live birth, 16% of newborns who died in that state had birth weights less than 500 g. Inconsistency in state definitions and possible variations in reporting live births less than 500 g affect state comparisons of infant and neonatal mortality rates.