Trends and Determinants of Acute Tocolysis Utilization in Japan: A Nationwide Retrospective Cohort Study

Background: Preterm birth remains a leading cause of neonatal mortality worldwide. While Japan has exceptionally low perinatal and neonatal mortality rates, clinical practice for preterm labor often involves maintenance tocolysis (MT) with ritodrine, which differs from international guidelines recommending acute tocolysis (AT) for up to 48 hours. To evaluate the current status of tocolytic practices in Japan, we investigated nationwide trends in the shift from MT to AT use and identify factors associated with the utilization of AT. Methods: This retrospective cohort study analyzed data from 156,356 pregnant women admitted to 720 institutions between April 2012 and March 2023 who received ritodrine infusion for preterm labor. Annual trends in AT utilization rates were examined, and logistic regression analysis was performed to identify factors associated with AT. Factors associated with AT use, including hospital characteristics, regional differences, and maternal obstetric complications, were explored. Results: The rate of AT utilization increased from 15.73% to 23.74% over the 11-year period, but variation among hospitals widened. University hospitals (adjusted odds ratio [aOR] = 1.16, p < 0.001), perinatal centers (aOR = 1.12, p < 0.001), preterm premature rupture of membranes (aOR = 3.18, p < 0.001), and pregnancy-induced hypertension (aOR = 1.52, p < 0.001) were associated with AT, while concomitant use of magnesium sulfate hydrate (aOR = 0.91, p < 0.001), multiple fetuses (aOR = 0.64, p < 0.001), and placenta previa (aOR = 0.67, p < 0.001) were negatively associated with AT utilization. Conclusion: While the rate of AT utilization has increased over time, differences in utilization exist between facilities, suggesting that choice of AT is influenced by multiple factors, including the perinatal medical system, maternal obstetric complications, and regional characteristics. Further discussion and research are needed to optimize treatment strategies to maximize maternal and fetal safety and improve outcomes. Trial registration: Not applicable.