The influence of socioeconomic status on stillbirth risk in Sweden.

BACKGROUND Low socioeconomic status (SES) is generally associated with increased risk of stillbirth, but the mechanisms have rarely been investigated. Our aim was to study the association between SES and risk of stillbirth, and to assess whether any differences in risk are mediated by other maternal socio-demographic or anthropometrical characteristics, differences in lifestyle, or attendance at antenatal care. METHODS Population-based individually-matched case-control study including 702 cases of stillbirth and 702 controls among Swedish primiparous women giving birth 1987-1996. We estimated the risk of stillbirth, and subgroups of stillbirth, for various categories of SES. Odds ratios (OR) with 95% CI, estimated by conditional logistic regression, were used to approximate the relative risk. The estimates were adjusted for maternal age, height, body mass index, cigarette smoking, and when necessary mother's country of birth. RESULTS Compared with women who were high level white-collar workers, the adjusted risks of stillbirth were as follows: unskilled blue-collar workers, 2.2 (95% CI : 1.3- 3.7), skilled blue-collar workers, 2.4 (95% CI : 1.3-4.1), low level white-collar workers, 1.9 (95% CI : 1.2-3.2), and intermediate level white-collar workers 1.4 (95% CI : 0.9-2.4). These risks were not substantially changed when we further adjusted for attendance at antenatal care, previous reproductive history, or excluded pregnancies with maternal diseases, and pregnancy-related disorders. Low social class was most associated with risks of term antepartum and intrapartum stillbirths. CONCLUSIONS Low SES increases the risk of stillbirth. The association could not be explained by any of the factors we studied, and the underlying reasons remain unclear.