Association of Maternal Nationality with Stillbirth and Infant Mortality: An Analysis of National Data in Japan.

Introduction: This study investigated the association of maternal nationality with stillbirth and infant mortality in Japan. Methods: The Vital Statistics data in Japan from 2010 to 2023 were used, and singleton births born from 2010 to 2022 were used in the analysis of stillbirth and infant mortality. The maternal nationality consisted of Japan, Korea, China, the Philippines, Thailand, the United States (US), Brazil, Peru, and other countries in the analysis. Stillbirth and infant mortality rates were calculated by maternal nationalities. In addition, modified Poisson regression models were used to investigate the associations between the outcomes and maternal nationality, and residential area, parity, maternal age, marital status, and year of birth were adjusted. Results: Data on 12,287,030 live births and 33,968 stillbirths were analyzed. As a result, the stillbirth rate for American mothers was the highest, and that of "other countries" was the second highest. In addition, the infant mortality rate of American mothers was also the highest. The multivariate regression analysis revealed that mothers from the US and "other countries" had a significantly higher risk of stillbirth than Japanese mothers and mothers from the US had a significantly higher risk of infant mortality than Japanese mothers. Conclusions: It was suggested that support before and after childbirth is particularly necessary for American mothers in Japan.