Conclusions
A reference line passing through the most inferior aspect of the pubic symphysis to the midpoint of the third sacral vertebra mostly conforms to a normal upper two-thirds of the vaginal axis, enabling the objective and accurate assessment of this part of the vagina in situ, which could be valuable for surgical planning, postsurgical follow-ups and assessing whether a repair surgery is more suitable. However, how to use this line as a reference for POP staging remains unclear, and further prospective studies are needed.