COMMENT
Several findings are notable from this retrospective, cohort study. First, when cervical dilation 1-6 cm in twins, ECC performed with the combined McDonald-Shirodkar procedure is of more benefit, with reduction in the rates of sPTB at <28, <30, <32 and <34 weeks, significantly prolongation of latency (8 weeks), higher GA at delivery, higher birth weight and lower perinatal mortality than with McDonald procedure. Second, when cervical dilation ≥ 3cm, combined McDonald-Shirodkar procedure has more obvious advantages with significantly reduction sPTB at <28 , <30 weeks, and overall perinatal mortality, also with prolongation pregnancy (by more than 6 weeks), greatly improved GA at birth, and higher birth weight compared with McDonald technology.
Some previous studies suggested no difference in outcomes when women receiving Shirodkar were compared with those receiving McDonald cerclages27 .15 ,16 ,22 . Also some researches indicated that Shirodkar superior to McDonald because of that the advantage of Shirodkar cerclage placed higher on the cervix.16 ,28 ,29 . However, all studies are committed to singleton pregnancy with cervical  incompetence,no well-designed studies comparing the efficacy of these methods for ECC in twin pregnancy have been published. Since the occurrence mechanism of sPTB is different between twin and singleton pregnancies24 ,30 ,31 , preventive measures should be treated differently. In addition to the patient population, cerclage position may effect the variability of cerclage efficacy, and higher cerclage is associated with a lower incidence of sPTB. Recently, Alper Basbug et al27 conducted a retrospective study compared the efficacy of modified Shirodkar and McDonald cerclage techniques in singleton pregnancy with cervical dilation>1cm, although they found there had no differences in rates of sPTB and GA at birth ,but the interval from cerclage to delivery was significantly longer in Shirodkar group than in McDonald group(83.8 ± 37.6 vs 63.7 ± 38.9 days, p=0.08) .Therefore, we can assume that ECC performed Shirodkar technique had longer pregnancy latency than McDonald technique, and in our study, we underwent combined McDonald-Shirodkar technique which involves the dissection of the bladder with suture placement as high as feasible around the supravaginal. Our research had indicated that this technology may reduce rates of sPTB and improve maternal and fetal outcomes when compared with McDonald technology.
In our cohort research, we used a 1-0 non-absorbable sutures when undergone McDonald’s technique and use a Mersilene tape when conducted Shirodkar technique, and in a RCT research on cervix cerclage materials suggested that monofilament suture did not reduce rate of pregnancy loss when compared with a braided suture32 . Zhi- Min Xu et al33 conducted a retrospective case-control study compare the efficacy of two stitches versus one stitch in women with ECC in singleton pregnancies and indicated that the procedure with two stitches can prolong the pregnancy and improve the neonatal prognosis more effectively, and it was similar to our research that we also use two stitches in case group. Resul Karakus et al34 reported a new a technique , using a combination of the Shirodkar and McDonald’s techniques to trying to place the Mersilene tape as high as possible on the uterine cervix for ECC and proposed this method is safe, effective, and had better fetal and neonatal outcomes in singleton pregnancies compared with McDonald method. But their study had a small sample size and all the cases in the study were singleton pregnancies.
The efficacy of cerclage was reduced in cases which cervical dilatation has begun and the fetal membranes have prolapsed into the vagina, because the larger the cervical dilatation, the higher the difficulty of operation and the higher the risk of failure23 ,35 ,36 . The currently available literature lack of evidence for cervical dilation of 4 cm or more, in 2019,SOGC10 suggested ECC may be considered in women in whom the cervix has dilated to < 4 cm without contractions. The only published study comparing ECC in twin pregnancies with cervical dilation 4-6cm showed an overall positive effect on pregnancy and neonatal outcomes37 , which indirectly supported a potential benefit of ECC in twin pregnancies with cervical dilation ≥ 4cm.
In our study, the cervical dilation was 1-6cm and more than 50% of cases with amniotic membranes prolapsed beyond the external os. And our conclusions were consistent with Chanjuan Zeng’s38 and we believed that in the urgent situation of cervical dilation of 4-6cm and bulging membranes, ECC may be the only salvage measure for prolonging gestation and improving neonatal outcome. In addition, our study assume that ECC performed with the combined McDonald- Shirodkar procedure is the best option of surgical therapy in twin pregnancies with cervical dilation of 3-6 cm and prolapsed membranes.
At present, most prior publications and guidelines on cervical cerclage suggest GA at cervical cerclage placement is up to 24 weeks of gestation. However, in clinical practice, prolongation of gestation can significantly improve neonatal prognosis and reduce perinatal mortality for women with asymptomatic cervical dilation≥ 1 cm or prolapsed membranes up to the external os at 24-26 weeks of gestation. And ,in 2022 ,RCOG14 suggested that ECC as a salvage measure in the case of premature cervical dilatation with exposed fetal membranes in the vagina can be considered up to 27+6 weeks of gestation. Resently, some retrospective cohort studies39 40 indicated that Ultrasound-indicated cervical cerclage (UIC) placement in twins may dilated to 26-28 week’s of gestation. And in our study, the GA of ECC placement extended to 26 weeks. Due to the small sample size, more large sample studies are needed to confirm this conclusion.