Objective: To explore the impact of dominant prolapse in other compartments in assessing bladder prolapse, and to establish cutoffs for staging bladder prolapse among Chinese women using translabial ultrasound. Design: Prospective multicentre observational study. Setting: Tertiary referral urogynaecology unit. Population: A total of 741 women with symptoms of lower urinary tract dysfunction and/or pelvic floor dysfunction were included. Methods: Women underwent interview, pelvic organ prolapse quantification (POP-Q) examinations and 4D translabial ultrasounds. Main outcome measures: The ROC statistic was used to assess accuracy and define the optimal cutoffs. Results: The mean patient age was 42.7 years (range, 18-82). There were 456 women without dominant prolapse in the apical/posterior compartments and 285 women with dominant prolapse in the apical/posterior compartments. Among patients without and with dominant prolapse, similar cutoffs (-10.9 mm vs. -9.1 mm) were determined for predicting POP-Q stage ≥ 2 in the anterior compartment, with AUCs of 0.87 and 0.79, respectively. In contrast, significantly different cutoffs (-5.7 mm vs. +3.5 mm) were determined for predicting POP-Q stage ≥ 1 among patients with and without dominant prolapse, with AUCs of 0.85 and 0.77, respectively. Conclusion: Dominant prolapse in the apical/posterior compartments affected the accuracy and cutoffs of translabial ultrasound for staging bladder prolapse. Thus, competition of various organs in women with multi-compartment prolapse should be considered as a potential complicating factor in assessing pelvic organ prolapse. Funding: The study is supported by grants from the National Natural Science Foundation of China (No. 91859115). Key words: Bladder prolapse; translabial ultrasound.