Infant mortality increase despite high access to tertiary care: an evolving relationship among infant mortality, health care, and socioeconomic change.

In this study, the determinants of an apparent increase in the infant mortality rate of an urban population with high access to tertiary neonatal care are reviewed. For a 4-year period (1980 to 1983), all infant deaths (n = 422) of the 32,329 births to residents of the City of Boston were analyzed through linked vital statistics data and a review of medical records. A significant increase in the infant mortality rate occurred in 1982 due to increases in three components of the infant mortality rate: the birth rate of very low birth weight infants (less than 1,500 g), the neonatal mortality rate of normal birth weight infants (greater than or equal to 2,500 g), and the mortality rate of infants dying during the postneonatal period (28 to 365 days). These increases were associated with inadequate levels of prenatal care. Although transient, the impact of the observed alterations in these infant mortality rate components was enhanced by a more long-standing phenomenon: the stabilization of mortality rates for low birth weight infants. This stabilization allowed the increases in other component rates to be expressed more fully than in previous years. In this report a mechanism is shown whereby fully regionalized neonatal care ultimately may confer to the infant mortality rate a heightened sensitivity to socioeconomic conditions and levels of adequate prenatal care.