[Maternal occupation and infant mortality in Japan: Insights from the Vital Statistics (Occupational and Industrial Aspects)].

Objectives　The proportion of Japanese women who maintain their employment during pregnancy and after delivery has been increasing. Previous studies from Western countries showed an association between the mother's occupation and birth outcomes; however, to the best of our knowledge, no epidemiological study has analyzed this association in Japan. Therefore, data from the national Vital Statistics: Occupational and Industrial Aspects were used to examine the association between the mother's occupation and (1) the risk of stillbirth at or after 12 weeks of gestation, and (2) the risk of infant death under 1 year of age after livebirth.Methods　Data from the Vital Statistics: Occupational and Industrial Aspects (Live Birth Form, and Foetal Death Form) for fiscal years (FYs) 1995, 2000, 2005, 2010, and 2015 and Vital Statistics data files (Death Form) from FYs 1995-96, 2000-01, 2005-06, 2010-11, and 2015-16 were analyzed. The study population consisted of (1) 5,355,881 infants who were born during the survey period, with (2) 5,290,808 live birth excluding still birth during the same period. The odds ratios (ORs) were estimated for (1) stillbirth (without stillbirth = livebirth) and (2) infant death (without infant death = alive at 1 year of age) by mother's occupation (managers/specialist/technical workers, clerical workers, sales workers, service workers, blue collar workers, and not employed) using logistic regression. Blue collar workers included workers in security, agriculture/forestry/fishing, manufacturing process, transport, and machine operation. The population attributable risk (PAR) for stillbirth attributed to mother's occupation among employed mothers was also calculated.Results　There were 61,179 (1.1%) stillbirths in the study population and 12,789 (0.2%) infant deaths among 5,290,808 live birth. Compared to managers/specialist/technical workers, the adjusted ORs (95% confidence interval) for stillbirth among clerical workers, sales workers, service workers, blue collar workers and not employed women were 1.24 (1.20-1.29), 1.48 (1.41-1.56), 1.76 (1.69-1.83), 1.54 (1.46-1.61), and 0.95 (0.92-0.98), respectively. There was no association between the mother's occupation and infant deaths. The PAR values for stillbirth among mothers employed as clerical workers and service workers were 7.4% and 12.3%.Conclusion　The risk of stillbirth differed according to the mother's occupation in our study. The OR and PAR of stillbirth were the highest for service workers. Mother's occupation was not associated with the risk of infant death; therefore, the mothers' occupation is likely to affect the children's condition only during pregnancy. Our study suggests the importance of understanding the causal linkage between pregnant women's occupation and birth outcomes.