Recent changes in maternal characteristics by socioeconomic status.

To describe changes in maternal characteristics by socioeconomic status, in order to provide a context for recent changes in the frequency of obstetric procedures and outcomes, and information for health planning purposes. All NS residents who delivered between 1988 and 2007 were included in the study. Information on maternal characteristics was obtained from the Nova Scotia Atlee Perinatal Database, and socioeconomic status information was obtained through a confidential link with federal income tax T1 Family Files (1988 to 2003). Total births to women < 20 years of age were high (31.5% in 2003) and increased in the lowest family income group between 1988 and 2003, while rates were low (0.7% in 2003) and decreased in the highest family income group. Total births to women >/= 35 years increased by 136% (95% CI 122, 150) between 1988-89 and 2006-07. Births to women with a weight >/= 90 kg also increased, while those to smokers decreased in all socioeconomic groups. The proportion of births to multiparous women with a previous low birth weight infant did not change (-5 %, 95% CI -14, 6), although births to women with a previous perinatal death declined by 52% (95% CI -60,-42). Large secular changes have occurred in maternal characteristics over the past two decades, and the magnitude of these changes has differed by socioeconomic status.