Population density and perinatal mortality in Norway and Sweden 1975-1988.

Data from the medical birth registries in Norway and Sweden were used to study geographical variations in perinatal mortality in the two countries. The study population comprised 1.4 million single births during 1975-79 and 1985-88. Perinatal death (n=9,834) for infants with a birthweight of 1,000 g or more was the main measure of outcome. In both periods and in both countries, perinatal mortality was inversely associated with population density and annual number of births, with relative risks amounting to 1.4 in Norway and 1.2 in Sweden. Among live births, these gradients were observed in deaths from asphyxia or immaturity in the first time period, and in deaths from congenital malformations in the second time period. As care for premature infants and infants with respiratory problems improves, geographical variations in perinatal mortality may to a larger extent depend on differences in medical care of infants affected by congenital malformations as well as differences in efforts to reduce the prevalence at birth of serious congenital malformations.