Study design and participants
In this retrospective cohort study, twin pregnancies were matched with the degree of cervical dilation at diagnosis. The patients in our study had comprised all twins with asymptomatic cervical dilation 1-6cm and/or with prolapsed membranes up to the external os at 18–26 weeks of gestation from December 2015 to December 2022 at four Medical Institutions: Women’s Hospital, Zhejiang University School of Medicine; Huzhou Maternity and Child Health Care Hospital; Shaoxing Maternity and Child Health Care Hospital; and The First People’s Hospital of Fuyang. The study was approved by the institutional Review Boards at each participating institution.
In case group, cerclage procedures were performed under a combination of the McDonald and Shirodkar’s techniques. Specific operations are as follows:
Firstly, using the McDonald’s technique with 1-0 non-absorbable sutures, under spinal anesthesia, the suture was not tightened,.A cervical balloon dilator (Aiyuan) was introduced to the cervical canal with gentle pressure to replace the membranes into the uterus before suturing, and the balloon at the top of the catheter was filled with 10-20 ml saline. Secondary, with the Shirodkar technique, a Mersilene tape was inserted above the junction of the cervix with dissection of the bladder and rectum and tried to place the tape as close to the internal cervical os as possible. Thirdly, remove the balloon slowly after drainng the saline, tightened the Mersilene tape first, then tighted the 1-0 non-absorbable suture.
A control group were matched one-to-one with the case group, according to the cervical dilation at diagnosis of ± 2 cm, GA of ±3 weeks at presentation of diagnosis and maternal age of ±5 years. We used case–control matching in Statistical Packages of Social Sciences (SPSS) for Windows, version 25.0 (SPSS, Chicago, IL, USA). Cerclage procedures were performed under McDonald’s techniques.
The decision to perform which cerclage technique was based on individual physician and patient preferences, and antenatal steroids were offered to all women ≥ 24 weeks of gestation. The exclusion criteria were included as follows: history of multi-fetal pregnancy reduction to twins at >14 weeks, fetuses with structural or chromosomal abnormalities, medically indicated PTB (twin-twin transfusion syndrome, severe preeclampsia, placental abruption, PPROM, or placenta previa), and cerclages placed for other indications (history-indicated cerclage or ultrasound-indicated cerclage). Patients who did not deliver in the four hospitals or were lost to follow-up by telephone were also excluded.