In Baden Walker Halfway system of classification of prolapse, the reference point is:
Baden walker halfway system STAGE DESCRIPTION 0 No descent of pelvis 1 leading edge of the prolapse remains 1cm or more above the hymenal ring II leading edge of the prolapse extends from 1 cm above to 1cm below the hymenal ring III From 1cm beyond the hymenal ring but without complete vaginal eversion IV Essentially complete eversion of vagina D.C.DUTTA&;S TEXTBOOK OF GYNAECOLOGY,Pg no:206,6th edition
Hymen
Introitus
Internal OS
External os
Urogynecology