ObjectiveThe aim of this study is evaluation of pregnancy outcomes of the asymptomatic cases with vaginal progesterone treatment for the 20−30 mm cervical length detected in the transvaginal ultrasonography for fetal abnormality screening and cervical cerclage after cervical length detected <20 mm in weekly cervical length measures; and present the treatment algorithm of progesterone treatment combined with cervical cerclage application. MethodsPatients who have the inclusion criteria and cervical length more than 30 mm were categorized as group 1(n = 1948). Group 2 were included patients with cervical length shorter than 30 mm (n = 95). All patients of group 2 started to use vaginal natural progesterone 400 mg/day(n = 87). Pregnancies which progressed with cervical length above 20 mm were continued vaginal progesterone until 34. Gestational week and they were named as group 2A (n = 78). Cervical cerclage were applied to patients with cervical length below than 20 mm measured via transvaginal ultrasonography and they were categorized as group 2B (n = 9). ResultsExcluding 8 cases (8.42 %) which cervical cerclage were applied, 87 patients were administered vaginal progesterone and in 9 cases (10.34 %) cervical shortening were continued despite progesterone treatment. Four out of these nine cases (44.44 %) had cervical cerclage and their deliveries were delayed after 34 th gestational week. Vaginal progesterone treatment prevented cervical shortening in 89.66 % of patients who had cervical length between 20−30 mm and out of these patients. ConclusionCervical cerclage application algorithm in continued cervical shortening cases despite vaginal progesterone is beneficial to delay the delivery after 34 th gestational week and related to low complication rate.