en Gynecology & Obstetrics Gynecology & Obstetrics Original Research Original Research <strong>&nbsp;&nbsp;</strong><strong>&nbsp; Background: </strong>The preterm labor has increased in multiple pregnancies over the past 2 decades. Preterm labor has led to increase in neonatal mortality rates, long-term morbidity, respiratory distress, and neonatal infections. Thus, this study aimed at investigating the effect of cerclage versus pessary on the prevention of preterm birth in twin pregnancies.<br> &nbsp;&nbsp; <strong>Methods: </strong>This prospective randomized clinical trial was performed on 50 women pregnant with twins who visited Taleghani hospital in 2016-2018. Their cervical length, which was measured by transvaginal ultrasonography (TVS), was less than 30 millimeters at week 14 of pregnancy. The participants were randomly divided into 2 groups (n=25). They separately underwent cervical pessary and cerclage. McDonald&#39;s procedure was performed in cerclage group from 14 to 27 weeks. The suture material was Mersilene Ethicon 5-0 double-armed s14 needle. Ring hodge pessary was also inserted in the vagina of the participants in the pessary group. All the patients were injected 250 mg intramuscular 17 alpha-hydroxyprogesterone caproate weekly from week 16 to week 36. All statistical analyses were performed using SPSS 18 software.<br> &nbsp;&nbsp; <strong>Results:</strong> The results of this study showed that the mean&thinsp;&plusmn;&thinsp;standard deviation (SD) for pregnancy length of the cerclage and pessary groups were 238.6&plusmn;32.4 and 223.6&plusmn;16.6, respectively. Also, significant differences were found between the 2 groups (p=0.048). No significant difference was found in pregnancy (p=0.565), length of pessary/cerclage use (p=0.491), and BMI before and after delivery between the cerclage and pessary groups (p>0.05).<br> &nbsp;&nbsp; <strong>Conclusion: </strong>The use of cerclage in twin pregnancies is recommended to increase the length of pregnancy. Cerclage, Pessary, Twin pregnancy 521 523 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-4988-1&slc_lang=en&sid=1 Nazanin Hajizadeh hajizadeh.nazanin94@yahoo.com 200319475328460064122 200319475328460064122 No Preventation Gynecology Research Center, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Nasrin Saharkhiz saharkhiz.n@sbmu.ac.ir 200319475328460064123 200319475328460064123 Yes Preventation Gynecology Research Center, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Sedigheh Hosseini s_s_hoseini58@yahoo.com 200319475328460064124 200319475328460064124 No Preventation Gynecology Research Center, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Behnam Arabzadeh behnamarabzade2000@gmail.com 200319475328460064125 200319475328460064125 No Anesthesiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran