SUMMARY OBJECTIVE: The aim of the study was to compare two labor induction regimens (4 and 6 h), to determine predictors of successful labor induction with intravaginal misoprostol 25 μg tablets, and to evaluate the association with adverse perinatal outcomes. METHODS: This was a retrospective cohort study that included singleton pregnancies undergoing induction of labor with an intravaginal misoprostol 25 μg tablet between 37 and 42 weeks of gestation. The pregnant women were divided into two groups: Group 1—intravaginal misoprostol 25 μg every 4 h and Group 2—intravaginal misoprostol 25 μg every 6 h. RESULTS: Pregnant women were divided into Group 1 (n=289) and Group 2 (n=278). Group 1 had a higher median number of intravaginal misoprostol 25 μg tablets (3.0 vs. 2.0 tablets, p<0.001), a lower prevalence of postpartum hemorrhage (7.6 vs. 32.7%, p<0.001), and a higher need for oxytocin (odds ratio [OR]: 2.1, 95%CI: 1.47–2.98, p<0.001) than Group 2. Models including intravaginal misoprostol 25 μg tablets every 4 and 6 h [x2(1)=23.7, OR: 4.35, p<0.0001], parity [x2(3)=39.4, OR: 0.59, p=0.031], and Bishop’s score [x2(4)=10.8, OR: 0.77, p=0.019] were the best predictors of failure of labor induction. A statistically significant difference between groups was observed between the use of the first intravaginal misoprostol 25 μg tablet at the beginning (Breslow p<0.001) and the end of the active labor phase (Long Hank p=0.002). CONCLUSION: Pregnant women who used intravaginal misoprostol 25 μg every 4 h had a longer time from the labor induction to the beginning of the active phase of labor and higher rates of adverse perinatal outcomes than women who used intravaginal misoprostol 25 μg every 6 h. OBJECTIVE ( h, , h) METHODS 3 gestation 1intravaginal 2intravaginal RESULTS n=289 n289 n 289 (n=289 n=278. n278 n=278 . 278 (n=278) 3.0 30 0 (3. vs 20 p<0.001, p0001 p p<0.001 001 7.6 76 7 (7. 327 32 32.7% odds OR [OR] 21 2.1 95%CI 95CI CI 95 147298 47 98 1.47–2.98 x21=23.7, x21237 x x2 =23.7, 23 [x2(1)=23.7 435 35 4.35 p<0.0001, p00001 p<0.0001 0001 p<0.0001] x23=39.4, x23394 =39.4, 39 [x2(3)=39.4 059 59 0.59 p=0.031, p0031 p=0.031 031 p=0.031] Bishops Bishop s x24=10.8, x24108 =10.8, 10 8 [x2(4)=10.8 077 77 0.77 p=0.019 p0019 019 Breslow Long p=0.002. p0002 p=0.002 002 p=0.002) CONCLUSION n=28 n28 28 (n=28 n27 n=27 27 (n=278 3. (3 p000 p<0.00 00 7. (7 32.7 [OR 9 14729 1.47–2.9 x21 x21=23.7 x2123 237 =23.7 [x2(1)=23. 43 4.3 p0000 p<0.000 000 x23 x23=39.4 x2339 394 =39.4 [x2(3)=39. 05 5 0.5 p003 p=0.03 03 x24 x24=10.8 x2410 108 =10.8 [x2(4)=10. 07 0.7 p=0.01 p001 01 p=0.00 n=2 n2 (n=2 (n=27 p00 p<0.0 32. 1472 1.47–2. x21=23. x212 =23. [x2(1)=23 4. x23=39. x233 =39. [x2(3)=39 0. p=0.0 x24=10. x241 =10. [x2(4)=10 n= (n= p0 p<0. 147 1.47–2 x21=23 =23 [x2(1)=2 x23=39 =39 [x2(3)=3 p=0. x24=10 =10 [x2(4)=1 (n p<0 14 1.47– x21=2 =2 [x2(1)= x23=3 =3 [x2(3)= p=0 x24=1 =1 [x2(4)= p< 1.47 x21= = [x2(1) x23= [x2(3) p= x24= [x2(4) 1.4 [x2(1 [x2(3 [x2(4 1. [x2( [x2 [x