Objective: To clarify the relationship between betamimetic administration duration and maternal adverse events (MAEs) Design: Retrospective cohort study Setting: A nationwide, acute-care hospital setting in Japan, using the Diagnosis Procedure Combination (DPC) database. Population: Pregnant women who were administered the betamimetic ritodrine hydrochloride (ritodrine) between April 2012 and March 2023 (n=96,991) Methods: We utilized the DPC database. Logistic regression analysis, adjusted for potential confounders, assessed the association between ritodrine duration (acute tocolysis [AT] ≤ 48 hours vs. maintenance tocolysis [MT] >48 hours) and MAEs. Main Outcome Measures: Comprehensive ritodrine-related MAEs: pulmonary oedema, heart failure, liver dysfunction, neutropenia, rhabdomyolysis, arrhythmia, foetal arrhythmia, hypokalaemia, hyperglycaemia, gestational diabetes mellitus (GDM), and venous thromboembolism (VTE). Results: Among 96,991 patients, 21.45% received AT and 78.55% MT. The incidence of MAEs, including VTE, GDM, liver dysfunction, hypokalaemia, rhabdomyolysis, and neutropenia, was higher in the MT than in the AT group. Logistic regression analysis showed that MT was associated with higher odds of VTE (odds ratio [OR] 1.61, p < 0.001), GDM (OR 3.23, p < 0.001), and liver dysfunction (OR 2.94, p < 0.001) than was AT. Meanwhile, AT was associated with heart failure and pulmonary oedema (OR 1.30, p < 0.042; OR 1.41, p < 0.043). Conclusions: These findings emphasize the need for careful maternal monitoring during ritodrine use, regardless of duration, to prevent severe side effects.