Objective To investigate the value of cervical posterior horn and progression angle measured by transperineal ultrasound in predicting vaginal delivery after induction of labor with dinoprostone thrombus in pregnant term primiparous women with Bishop score＜4 points.Methods Selected pregnant term primiparous women who underwent induction of labor between June 2021 and June 2022 in Anhui maternal and child health hospital，using dinoprostone thrombus to induce cervical ripening induction of labor，divided into vaginal delivery group and cesarean section group according to the induction outcomes，compared the two groups of general information and ultrasound before induction of labor，determined the indicators that had the independent predictive ability for vaginal delivery after induction using logistic regression analysis，assessed the predictive efficacy of the indicators using ROC curve，The Youden index was used to determine the optimal threshold value of the index，and the sensitivity and specificity were calculated.Results A total of 381 parturients were included in the final analysis，of whom 335 were delivered vaginally and 46 by cesarean section，compared with the cesarean section group，and the parturients in the vaginal delivery group had a younger age，a shorter cervix，and a greater posterior cervical horn and rudimentary horn，with statistically significant differences （P＜0.05）.Logistic regression analysis showed that the posterior cervical horn （or：0.948，95% CI：0.932-0.964，P = 0.000） and the progressive horn （or：0.955，95% CI：0.920-0.991，P =.0015） were independent predictors of vaginal birth after induction of labor. ROC curve analysis showed that the sensitivity

specificity

and area under curve of posterior cervical angle predicting vaginal delivery after induced labor were 68.40%

84.80%

and 0.843 (95% confidence interval: 0.782~0.904). The sensitivity

specificity and AUC of angle of progression predicting vaginal delivery after induced labor were 82.10%

50.00% and 0.652 (95% confidence interval: 0.554~0.750). The area under the curve of posterior cervical angle was higher than that of angle of progression

and the differences were statistically significant (P=0.001).Conclusion For pregnant term primiparous women with a Bishop score＜4 points，the posterior cervical horn，and progression angle were independent predictors of vaginal delivery after induction of labor，and the predictive efficacy of the posterior cervical horn was better.