Risk factors of early spontaneous abortions among Japanese: a matched case-control study

BACKGROUND: No epidemiological studies have examined risk factors for early spontaneous abortions among Japanese women. In this matched case-control study, we investigated the associations of reproductive, physical, and lifestyle characteristics of women and their husbands with early spontaneous abortion < 12 weeks of gestation. METHODS: Information was collected through medical records for 430 cases of early spontaneous abortion and 860 controls of term delivery. Two controls were individual-matched to one case according to maternal age (+/- 3 years) and calendar year of events (either early spontaneous abortion or delivery). Multivariable conditional odds ratios (ORs) and 95% confidence interval (CI) were calculated with conditional logistic-regression. RESULTS: The risk of early spontaneous abortions was higher for women with a past history of early spontaneous abortions; OR was 1.98 (95% CI: 1.35, 2.89) for one previous spontaneous abortion, 2.36 (95% CI: 1.47, 3.79) for two, and 8.73 (95% CI: 5.22, 14.62) for three or more. Other factors also influence risk; an OR of 2.39 (95% CI: 1.26, 4.25) was found for women who smoked, and 1.65 (95% CI: 1.17, 2.35) for women working outside the home. CONCLUSIONS: Our finding suggests that for Japanese women, smoking and working may be important public health issue targets for the prevention of early spontaneous abortions.