Introduction
Twins account for 0.5–4.0% of all births, in the last decade, the rate of twin pregnancies has increased substantially in China1 2 ,3 . During 2012 to 2020, the twinning rate increased by 13.3% from 2.84 to 3.22 per 100 total births4 . Since fertility policy had changed in China from two-child policy in 2014 and three-child policy in 2021, the rate of multiple births has shown an upwards trend5 .Twin pregnancies are associated with 50% incidence of preterm birth (PTB) and at increased risk for low birth-weight (LBW), they are five times more likely to have early neonatal and infant death and complications related to prematurity and LBW6 The most important risk factor for PTB in twins is short cervical length prior to 24 weeks7-9 . Twin pregnancies with cervical dilation ≥1cm in the second trimester are associated with a poor prognosis, and more than 90% will result in sPTB10-13 . The data on the efficacy of cervical cerclage based on dilated cervix is limited in twin pregnancies, whereas it is widely accepted in singleton pregnancies. In 2019, the Society of Obstetricians and Gynaecologists of Canada (SOGC)10 and in 2022 ,the Royal College of Obstetricians Gynaecologists (RCOG)14 suggested that emergency cervical cerclage (ECC) as a salvage measure in both singleton and multiple gestations, when the cervix is dilated to >1cm without contractions. So ECC represents one of the best-commonly surgical interventions to prevent sPTB in obstetrics. While the technique has been widely studied and evaluated, controversy remains regarding certain aspects of the therapeutic indication and complementary management tests to be performed15-20 . Currently, two most commonly performed cerclage procedures are modifications of Shirodkar and McDonald21 ,22 . ECC may have higher chance of failure and other complications such as preterm premature rupture of membranes (PPROM), chorioamnionitis are more common23 ,24 . It has been suggested that cerclage placement closer to the internal os may be associated with improved perinatal outcome25 ,26 . Unlike the known methods, our novel technique is characterized by a combination of the Shirodkar and McDonald’s techniques, application of a cervical balloon dilator (Aiyuan) to replace the membranes into the uterus before placement of Shirodkar suture. The aim of our research is to compared the effectiveness of this novel technique to McDonald method, and to observe whether this ECC technology has the best maternal and neonatal outcomes in twins with cervical dilation of 1-6cm and/or prolapsed membranes without contraction between 18-26 weeks of gestation.