INTRODUCTION: The purpose of this study was to evaluate whether there are additional benefits of 17-hydroxyprogesterone caproate (17-OHPC) supplementation in preventing recurrent spontaneous preterm birth in women with a prophylactic cerclage. MATERIAL AND METHODS: Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, PROSPERO, EMBASE, Scielo and the Cochrane Central Register of Controlled Trials) were searched for studies published before June 2018. Keywords included "preterm birth", "prophylactic cerclage", "history-indicated cerclage", "pregnancy" and "17-hydroxyprogesterone caproate". Studies comparing history-indicated cerclage alone with cerclage+17-OHPC were included. The primary outcome measure was preterm birth at <24 weeks of gestation. Secondary outcome measures include preterm birth at <28 weeks, <32 weeks and <37 weeks of gestation, respiratory distress syndrome, necrotizing enterocolitis, fetal birthweight, neonatal intensive care unit stay, mean gestational age at delivery, fetal/neonatal death, neurological morbidity (intraventricular hemorrhage plus periventricular leukomalacia), neonatal sepsis and a composite of severe neonatal morbidity. Severe neonatal morbidity was defined as a composite measure of periventricular leukomalacia, intraventricular hemorrhage (grades III and IV), necrotizing enterocolitis or respiratory distress syndrome. Meta-analysis was performed using the random-effects model of DerSimonian and Laird. Risk of bias and quality assessment were performed using the ROBINS-I and GRADE tools, respectively. PROSPERO Registration Number: CRD42018094559. RESULTS: Five studies met the inclusion criteria and were included in the final analysis. Of the 546 women, 357 (75%) received history-indicated cerclage alone and 189 (35%) received adjuvant 17-OHPC. The composite endpoint, severe neonatal morbidity, was present in 84 of 1515 neonates. Though there was a trend toward a reduced risk of preterm birth, the summary estimate of effect was not statistically significant when comparing cerclage alone with cerclage+17-OHPC at <24 weeks (relative risk [RR] .86, 95% confidence interval [CI] .45-1.65). Similarly, we found no differences in preterm birth at <37 weeks (RR .90, 95% CI .70-1.17) and <28 weeks (RR .85, 95% CI .54-1.32) when comparing cerclage alone with cerclage+17-OHPC. There were no differences in fetal birthweight, respiratory distress syndrome or necrotizing enterocolitis comparing cerclage alone with cerclage+17-OHPC. CONCLUSIONS: Intramuscular 17-OHPC in combination with prophylactic cerclage in women with prior preterm birth had no synergistic effect in reducing spontaneous recurrent preterm birth or improving perinatal outcomes.