Changing patterns of inequality in birthweight and its determinants: a population-based study, Scotland 1980-2000

Birthweight is used as an indicator of individual and population health and is known to be strongly correlated with adult cardiovascular disease. This paper uses routinely collected maternity discharge data from Scotland between 1980 and 2000 to look at birthweight trends and the changes in the distribution of maternal risk factors for birthweight. We also examine the contributions of each of the risk factors to birthweight trends and investigate whether there has been a reduction in inequality in birthweight over time. Data from 1,282,172 singleton live births were used in the analysis. Both mean birthweight and low birthweight (LBW:<2500 g) were used as outcomes. The risk factors studied were maternal age, parity, maternal height, marital status and occupational social class of the father. The slope and relative indices of inequality were used to measure the change in inequalities over time. Mean birthweight increased from 3320 g in 1980 to 3410 g in 2000, while the percentage LBW decreased slightly from 5.7% in 1980 to 5.4% in 2000. The prevalence of many risk factors changed; there has been an increase in the proportion of older mothers, single mothers, taller mothers and mothers with undetermined social class. Although most risk factors had a significant change in effect over time, the inequalities in birthweight between groups did not appear to diminish over time. Both the slope and relative index of inequality had a quadratic relationship over time, with the inequalities in birthweight being greatest in the early 1980s and late 1990s.