2. Randomization and masking
Patients were allocated (1:1:1) to one of three treatment arms: MA alone (control group), LNG-IUS alone, or MA+LNG-IUS group by the simple randomization. Randomization sequences were prepared according to random-number tables. The treatment allocation was concealed before the participants were successfully enrolled. This study was open-labelled that all patients and study physicians were aware of the treatment assignment. None of the clinicians who performed the hysteroscopic evaluation on patients in this trial and none of the pathologists who assessed the specimens from this trial was aware of the treatment allocations.