To investigate the efficacy of transvaginal cerclage in twin pregnancies with cervical shortening, and to narrow the threshold cervical length for transvaginal cerclage.This is a prospective cohort study and 177 twin pregnancies with asymptomatic cervical dilatation or cervical length of 15 mm or less between 16+0 and 25+6 weeks of pregnancy were included. Patients independently chose either transvaginal cerclage (n = 129) or no cerclage treatment (n = 48) after being consulted on the risk and potential benefit of transvaginal cerclage. The primary outcome measures were gestational age at delivery and neonatal survival rate.Compared with the no cerclage group, the cerclage group exhibited a higher gestational age at delivery (32.1 ± 4.5 vs 28.3 ± 6.2 weeks, P < 0.001) and a higher neonatal survival rate (86.4% vs 47.9%, P < 0.001). Subgroup analysis showed that in twin pregnancies with cervical dilatation or cervical length less than 10 mm, the cerclage group had significantly higher gestational age at delivery (31.3 ± 4.6 vs 23.4 ± 4.3 weeks, P < 0.001) and a higher neonatal survival rate (123 [85.4%] vs 4 [9.1%], P < 0.001) than the no cerclage group, but in twins when cervical length was 10-15 mm, the two measures were similar between the two groups.Transvaginal cerclage may provide benefits for twins when cervical dilatation or cervical length is less than 10 mm, but its efficacy might not extend to twins when the cervical length is 10-15 mm. Further evidence is needed to confirm the efficacy of transvaginal cerclage for twin pregnancies with a short cervix.© 2023 International Federation of Gynecology and Obstetrics.