The stages of prolapse are defined in relation to the opening of your vagina.
Stage 0: No prolapse is demonstrated.Stage I: The lowest part of the prolapse is more than 1cm above the level of the hymen (vaginal opening.)
Stage II: The lowest part of the prolapse sits between 1 cm above hymen and 1cm below the hymen.
Stage III: The lowest part of the prolapse is more than 1cm beyond the hymen.
Stage IV: Complete prolapse of the total length of the vagina. (Source)