A decade of decline and regional disparity: Trends and associated factors in use of ritodrine hydrochloride for threatened preterm labor in Japan, a nationwide ecological study

OBJECTIVE: Ritodrine hydrochloride is a commonly used tocolytic agent for threatened preterm labor in Japan, despite its serious adverse events and limited use in many other countries. National obstetric guidelines have shifted toward restricting its use, but the evidence-practice gap remains unclear. The aim of this study is to determine usage trends for ritodrine at nationwide and prefectural levels and identify factors associated with usage. METHODS: We conducted an ecological study linking nationwide aggregated medical claims data and statistical survey records across all 47 prefectures. We investigated 10-year trends in ritodrine use from fiscal year (FY) 2014 to 2023. Choropleth maps and spatial statistics illustrated geographic relationships among neighboring prefectures. We also conducted a cross-sectional study to identify factors associated with ritodrine injection use. RESULTS: The usage rate of ritodrine injection per 1000 deliveries decreased by more than 45% over 10 years. Joinpoint regression analysis identified FY2017 as a turning point, after which the decline accelerated. However, prefectural usage varied up to 13.58-fold, with spatial clustering of high-use regions. Factors associated with injection usage included the density of Perinatal Medical Centers (PMCs), hospital admissions for threatened preterm labor and preterm birth per 1000 deliveries, and the proportion of hospitals among delivery facilities. CONCLUSION: This study showed that nationwide use of ritodrine injection decreased by half over a decade, along with regional disparities among prefectures in Japan. These variations might reflect localized treatment policies influenced by differences in healthcare resources and geographical accessibility.