Objectives: Prior research has not yet examined the relationship between post-term birth and neonatal mortality in Japan, along with factors associated with post-term birth. We investigated these associations utilizing nationwide birth data from Japan. Methods: Birth and mortality data were obtained from the Vital Statistics of Japan for the years 2017 to 2022. The post-term birth rate was calculated by birth characteristics, and the neonatal mortality rates for post-term and term births were computed. Additionally, log-binomial regression analysis was employed to explore the associations between post-term birth and neonatal mortality, as well as between various characteristics and post-term birth. The characteristics considered included infant sex, maternal age group, parity, maternal nationality, maternal marital status, and household occupation. Results: This study analyzed data from 4 698 905 singleton infants born at 37 weeks of gestational age or later. Regression analysis revealed that post-term birth was positively associated with neonatal mortality. The adjusted risk ratio for neonatal mortality in post-term compared to term births was 8.07 (95% confidence interval, 5.06 to 12.86). Factors positively associated with post-term birth included female infant sex, older maternal age, primiparity, non-Japanese maternal nationality, unmarried status, and various household occupations, including farmer, full-time worker at a smaller company, other type of worker, and unemployed. Younger maternal age was inversely associated with post-term birth. Conclusions In Japan, post-term birth represents a risk factor for neonatal mortality. Additionally, socio-demographic characteristics, such as maternal marital status, nationality, and parity were found to be predictors of post-term birth.

As few studies have explored the association between non-regular or precarious employment in parents and adverse birth outcomes, this study aimed to investigate this association using national data in Japan.

As few studies have explored the association between non-regular or precarious employment in parents and adverse birth outcomes, this study aimed to investigate this association using national data in Japan.

Objectives: Prior research has not yet examined the relationship between post-term birth and neonatal mortality in Japan, along with factors associated with post-term birth. We investigated these associations utilizing nationwide birth data from Japan. Methods: Birth and mortality data were obtained from the Vital Statistics of Japan for the years 2017 to 2022. The post-term birth rate was calculated by birth characteristics, and the neonatal mortality rates for post-term and term births were computed. Additionally, log-binomial regression analysis was employed to explore the associations between post-term birth and neonatal mortality, as well as between various characteristics and post-term birth. The characteristics considered included infant sex, maternal age group, parity, maternal nationality, maternal marital status, and household occupation. Results: This study analyzed data from 4 698 905 singleton infants born at 37 weeks of gestational age or later. Regression analysis revealed that post-term birth was positively associated with neonatal mortality. The adjusted risk ratio for neonatal mortality in post-term compared to term births was 8.07 (95% confidence interval, 5.06 to 12.86). Factors positively associated with post-term birth included female infant sex, older maternal age, primiparity, non-Japanese maternal nationality, unmarried status, and various household occupations, including farmer, full-time worker at a smaller company, other type of worker, and unemployed. Younger maternal age was inversely associated with post-term birth. Conclusions In Japan, post-term birth represents a risk factor for neonatal mortality. Additionally, socio-demographic characteristics, such as maternal marital status, nationality, and parity were found to be predictors of post-term birth.

As few studies have explored the association between non-regular or precarious employment in parents and adverse birth outcomes, this study aimed to investigate this association using national data in Japan.

Objectives: Prior research has not yet examined the relationship between post-term birth and neonatal mortality in Japan, along with factors associated with post-term birth. We investigated these associations utilizing nationwide birth data from Japan. Methods: Birth and mortality data were obtained from the Vital Statistics of Japan for the years 2017 to 2022. The post-term birth rate was calculated by birth characteristics, and the neonatal mortality rates for post-term and term births were computed. Additionally, log-binomial regression analysis was employed to explore the associations between post-term birth and neonatal mortality, as well as between various characteristics and post-term birth. The characteristics considered included infant sex, maternal age group, parity, maternal nationality, maternal marital status, and household occupation. Results: This study analyzed data from 4 698 905 singleton infants born at 37 weeks of gestational age or later. Regression analysis revealed that post-term birth was positively associated with neonatal mortality. The adjusted risk ratio for neonatal mortality in post-term compared to term births was 8.07 (95% confidence interval, 5.06 to 12.86). Factors positively associated with post-term birth included female infant sex, older maternal age, primiparity, non-Japanese maternal nationality, unmarried status, and various household occupations, including farmer, full-time worker at a smaller company, other type of worker, and unemployed. Younger maternal age was inversely associated with post-term birth. Conclusions In Japan, post-term birth represents a risk factor for neonatal mortality. Additionally, socio-demographic characteristics, such as maternal marital status, nationality, and parity were found to be predictors of post-term birth.

Objectives: We investigated trends in the incidence rate of macrosomia and its association with parental nationalities using Vital Statistics data in Japan. Methods: We used singleton birth data every 5 years from 1995 to 2020. The incidence rate of macrosomia was calculated according to specific attributes (maternal age, infant’s sex, parental nationalities, parity, and household occupation) over time (years). In addition, a log-binomial model was used to investigate the relationship between the incidence of macrosomia and the attributes. This study compared Korea, China, the Philippines, Brazil, and other countries with Japan in terms of parental nationalities. “Other countries” indicates countries except for Japan, Korea, China, the Philippines, and Brazil. Results: The study included 6 180 787 births. The rate of macrosomia in Japan decreased from 1.43% in 1995 to 0.88% in 2020, and the decrease was observed across all parental nationalities. The rates for Japanese parents were the lowest values among parental nationalities during the timespan investigated. Multivariate regression analysis showed that mothers from Korea, China, the Philippines, Brazil, and other countries had a significantly higher risk of macrosomia than those from Japan (risk ratio, 1.91, 2.82, 1.59, 1.74, and 1.64, respectively). Furthermore, fathers from China, the Philippines, Brazil, and other countries had a significantly higher risk of macrosomia than those from Japan (risk ratio, 1.66, 1.38, 1.88, and 3.02, respectively). Conclusions The rate of macrosomia decreased from 1995 to 2020 in Japan for parents of all nationalities, and the risk of macrosomia incidence was associated with parental nationality.