Background: International rankings of infant mortality rates have been consistently lower for the US than other industrialized countries, and this ranking has been falling. This study examines the influence of birth registrations among very low birthweight infants on these international rankings.
Methods: Birth rates of infants weighing < 1500 g (VLBW) reported by Japan, Sweden, the Netherlands, France, the UK and Canada were compared to the rates of infants of this weight born in the US, and these rates were correlated with the infant mortality rates reported by these countries. Also, deaths in the first 24 hours after birth were correlated with the reported mortality rates.
Results: Countries with the lowest infant mortality rates tended to have the lowest incidence of births < 500 g (correlation coefficient, r = 0.73) and of births 500-999 g (correlation coefficient, r = 0.81). When white and black newborns in the US were reported separately, the correlation coefficients were 0.96 and 0.97 for these weights. Furthermore, the countries with the lowest infant mortality rates registered the fewest number of deaths in the first 24 hours after birth, correlation coefficient, r = 0.78; when white and black newborns were reported separately, r = 0.95. In addition, the international rankings of the US, 1969-1988, when correlated with the annual birth rate of white infants < 500 g registered in this country was r = 0.78.
Conclusion: Differences in birth registration practices for infants weighing < 1500 g are primarily responsible for the poor, deteriorating performance by the US in the international rankings of neonatal mortality rates.