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143: The confounding influence of domicile and ethnicity on infant mortality

      Objective

      Infant mortality and stillbirth rates are higher among status Indians (SI) in British Columbia (BC), Canada. Less is known of the effect of domicile on these rates. To examine the confounding influence of domicile on stillbirth and infant mortality (IM) among SI compared to non-SI infants. Domicile characteristics used were A) rural/urban residence (<10,000 inhabitants vs more); B) distance from and C) mode of transportation (road/air/ferry) to a level2/3 hospital. We adjusted for other covariates: prenatal care, parity, multiple births, congenital anomalies, maternal age, marital status, low-income neighbourhood, smoking, alcohol and drug use, obstetric history, and infant′s sex.

      Study Design

      Retrospective cohort study including all BC births between 1999-2004. Vital statistics identified SI and deaths. All other fields came from the BC Perinatal database. Postal codes determined domicile categories. We calculated relative risks (RR) and logistic regression adjusted Odds Ratios (adjOR) and their 95% confidence intervals (CI).

      Results

      Of the 158,136 births, 9199 (5.8%) were SI. Stillborn were 0.71% SI and 0.47% non-SI infants (RR=1.3, CI:1.1-1.6). The IM was 8.7 (SI) and 3.9 (non-SI) per 1000 live births (RR=2.2, CI:1.7-2.7). Prematurity (SI infants) and congenital anomalies (non-SI infants) were the main causes of IM. RR of stillbirth remained similar by domicile. The RR of IM for SI infants changed: 3.2 (CI:2.1-4.8) in rural vs 2.0 (CI:1.5-2.6) in urban areas; 2.1 (CI:1.6-2.8) at 50km vs 2.8 (CI:1.7-4.4) at >50km distance from hospital; and 2.1 (CI:1.6-2.7) for road vs 4.6 (CI:1.4-15.2) for ferry/air transportation. Accounting for other covariates, the adjOR for IM was 1.5 (CI:1.1-2.0), for stillbirth 1.0 (CI:0.8-1.4).

      Conclusion

      SI infants in rural/remote areas have a higher risk of death. Adjusting for domicile decreases but does not remove the increased risk; however, it removes the increased risk of stillbirth. Further research is needed to examine why more SI infants are born preterm.