Objective:To investigate the effectiveness and safety of low-dose oral misoprostol solution for cervical ripening in late gestation.Methods:This was a prospective cohort study including 396 primiparas with singleton pregnancy who received low-dose oral misoprostol solution for cervical ripening (oral group) in Peking University Third Hospital from March to October 2022. They were further allocated to receive oral misoprostol alone (OA group, n=167) or oral misoprostol in combination with oxytocin/amniotomy (OC group, n=229). Moreover, 218 cases who received vaginal misoprostol for cervical ripening (vaginal group) during the same period in 2021 were reviewed (a retrospective cohort). Among them, 77 were given vaginal misoprostol alone (VA group) and 141 received vaginal misoprostol in combination with oxytocin/amniotomy (VC group). The OA group and VA group (72 and 73 cases) as well as the OC group and VC group (108 and 103 cases) were matched using propensity scores. Basic clinical information, hospital stay, duration of labor induction, uterine hyperstimulation, rate of labor initiation, vaginal delivery rate, rate of delivery within 24 h, duration of labor, neonatal condition, adverse pregnancy outcomes, and other information were compared between different groups. All data were statistically analyzed using independent sample t test, analysis of variance, nonparametric test, Chi-square test, or Fisher's exact probability test. Logistic regression model was used to analyze the factors affecting the labor initiation and the failure of labor induction. Results:The average hospital stay, the duration from medication to labor initiation and the duration from medication to vaginal delivery were significantly shorter in the oral group than those in the vaginal group [(5.4±2.4) vs. (6.5±2.6) d, (34.2±24.1) vs. (38.9±25.7) h, (45.8±25.8) vs. (53.4±27.8) h; t=5.24, 2.10 and 3.39; all P<0.05]. The total labor initiation rate and vaginal delivery rate in the oral group were significantly higher than those in the vaginal group [92.9% (368/396) vs. 83.5% (182/218), 72.2% (286/396) vs. 60.1% (131/218); χ 2=13.43 and 9.50; both P<0.05]. The incidence of failed induction of labor, uterine hyperstimulation, fetal distress, and intrauterine infection in the oral group were lower than those in the vaginal group [2.0% (8/396) vs. 6.9% (15/218), 4.3% (17/396) vs. 17.9% (39/218), 8.8% (35/396) vs. 14.7% (32/218), 1.3% (5/396) vs. 3.7% (8/218); χ 2=9.21, 31.36, 4.93 and 3.93; all P<0.05]. The duration from medication to labor initiation and to vaginal delivery in the OA group were higher than those in the VA group [(25.8±17.0) vs. (17.4±10.8) h, (37.2±18.8) vs. (29.7±13.5) h; t=3.49 and 2.74; both P<0.05]. There were no significant differences in the labor initiation rate, vaginal delivery rate, rate of delivery within 24 h or the incidence of failed induction of labor between the OA and VA groups (all P>0.05). Women in the VA group were more likely to develop uterine hyperstimulation than those in the OA group [19.2% (14/73) vs. 4.2% (3/72), χ2=7.89, P=0.005]. There were no significant differences in the duration from medication to labor initiation or to vaginal delivery between the VC and OC groups (both P>0.05), but the duration were significantly longer than those in the corresponding medication alone group (VC vs. VA groups: (49.7±24.6) vs. (17.4±10.8) h and (61.6±25.7) vs. (29.7±13.5) h, t=5.31 and 5.13, both P<0.05; OC vs. OA groups: (45.3±26.6) vs. (25.8±17.0) h and (56.1±27.2) vs. (37.2±18.8) h, t=10.35 and 9.78, both P<0.05]. The labor initiation rate, vaginal delivery rate and rate of delivery within 24 h in the OC group were higher than those in the VC group [88.9% (96/108) vs. 77% (87/113), 63.0% (68/108) vs. 47.8% (54/113), 10.3% (7/108) vs. 0.0% (0/113); χ 2=5.49, 5.14 and 7.56; all P<0.05]. The incidence of uterine hyperstimulation in the OC group was 4.6% (5/108), which was lower than that in the VC group [18.6% (21/113), χ 2=10.37, P=0.001]. Logistic regression analysis showed that oral misoprostol and gestational age were positively correlated with labor initiation [ OR (95% CI): 2.18 (1.24-3.90) and 1.43 (1.14-1.79)], while maternal age was negatively correlated with labor initiation [ OR (95% CI): 0.90 (0.82-0.98)]. Moreover, failed induction of labor was negatively correlated with oral misoprostol [ OR (95% CI): 0.37 (0.14-0.91)], but positively correlated with maternal age [ OR (95% CI): 1.21 (1.05-1.40)]. Conclusions:Oral administration of low-dose misoprostol solution is as effective as vaginal misoprostol in promoting cervical ripening. Besides, it can shorten the average hospital stay and reduce the incidence of uterine hyperstimulation, suggesting that low-dose oral misoprostol solution is relatively safer and can be used to promote cervical ripening in late gestation.