Why was the perinatal mortality rate higher in Denmark than in Sweden? The development in the 1970s and 1980s.

Abstract

The purpose of this article is to identify factors explaining why the perinatal mortality rate ceased to fall in Denmark during the 1980s, while it continued to do so in Sweden, and to study the ability of known risk factors to predict this development. My analysis is based on routinely collected published data on all births, where I have studied the levels and changes in known risk factors for perinatal deaths in the two countries. The results of the study are: The proportion of low birth weight infants and the mothers' age and parity did not differ or change in a way that explains the higher perinatal mortality rate in Denmark during the 1980s. The weight specific perinatal mortality rate was the same in the two countries, with the exception of very low birth weight babies, i.e. below 1,500 grammes, where the perinatal mortality rate was higher in Denmark; this difference increased during the 1980s. The proportion of very low birth weight infants increased in Denmark from the 1970s to the 1980s while it remained stable in Sweden. The Danish increase in the proportion of low birth weight infants can be due to changed registration practices with more very small infants being registered in the 1980s. Among the factors studied registration practices, smoking and neonatal care seemed to be able to explain part of the differences between the two countries. The relative risk of perinatal death associated with the mothers' age and parity varied depending on the size of the groups at risk: the more women in high age and parity groups the lower the relative risk, which indicates that a selection as well as a causal effect was present. A conclusion is that the changes in relative risk over time associated with age and parity should lead to a closer investigation of the characteristics actually associated with an increased risk in order not to treat all old and multiparous women as patients at risk.