【Abstract】Objective: To quantitatively evaluate the effect of vaginal delivery on the elasticity of levator ani muscle in primiparas by shear wave elastography (SWE), and to explore the value of levator ani muscle elasticity parameters in the early diagnosis of postpartum POP and to construct a clinical prediction nomogram model. Methods :A total of 107 primiparas who had vaginal delivery 42 days after delivery and underwent pelvic floor ultrasound examination in our hospital were enrolled. pelvic organ prolapse quantification (POP-Q) was used as the gold standard for the diagnosis of POP. Primiparas were divided into maternal POP positive group and maternal POP negative group. SWE was used to measure the elasticity values of the puborectal musclerE1, cE1, rE2, cE2, and the elasticity values of the iliococcygeus muscle rE3, cE3, rE4, cE4 at rest and in the state of anal contraction, and the differences of ΔE1, ΔE2, ΔE3, ΔE4 before and after anal contraction were calculated. First, the measurement parameters were compared within and between groups. Then, a nomogram clinical prediction model with multiple preferred parameters for the diagnosis of POP was established, the Bootstrap method was used for internal validation of the model, and the calibration curve was used to evaluate the diagnostic efficiency of the model. Results: 1. There were significant differences in the elasticity values of puborectalis and iliococcygeal muscles and the difference before and after anal contraction among the POP-positive group, POP-negative group at rest and during anal contraction (P < 0.05). 2. Taking cE1, cE4 and ΔE2 as the optimal elasticity parameters to establish a multi-parameter prediction model for the diagnosis of POP in primiparas. When the cut-off value was 0.48 (corresponding to a total score of 108 points), the sensitivity and specificity were 93.8% and 90.5%, respectively, and the AUC was 0.952 (95%CI=0.910-0.993). Internal validation (AUC=0.952) and calibration curve showed that the model had high predictive ability. Conclusion: 1. The damage to the elasticity of levator ani muscle caused by vaginal delivery in primiparas can lead to POP to some extent. 2.SWE can quantitatively evaluate the change of levator ani muscle elasticity in the early postpartum period. 3. The nomogram prediction model based on multiple optimal elasticity parameters of levator ani muscle is helpful for the early diagnosis of POP in primiparas, and the diagnostic efficiency of multiple parameters is better than that of single parameter.