Rust 2000.

Methods	RCT. May 1998 to August 2000. Lehigh Valley Hospital Outpatient Perinatal Testing Center. USA
Participants	Participants (N = 61): “Any patients between the gestational ages of 16 and 24 weeks with transvaginal ultrasound demonstration of (1) dilatation of the internal os, (2) prolapse of the membranes into the endocervical canal but not beyond the external os, (3) a shortened distal cervical length, and (4) exacerbation of these 3 findings associated with transfundal pressure was considered a candidate for enrolment”. Inclusion criteria: “Inclusion criteria consisted of demonstrable dilatation of the internal os and either prolapse of membranes at least 25% of the total cervical length or a distal cervical length of < 2.5 cm”. “Those patients, who met the inclusion criteria and provided informed consent, underwent an amniocentesis to rule out infection.” “A rescue arm of the study was designed for each group. Any patient at < 24 weeks. gestation who had prolapsed membranes beyond the level of the cerclage or to the external os (without cerclage) was offered a revision, or rescue cerclage procedure”. Exclusion criteria: “Exclusion criteria included membrane prolapse beyond the external os, any fetal lethal congenital or chromosomal anomaly, clinical evidence of abruption placenta, unexplained vaginal bleeding, chorioamnionitis (diagnosed by clinical or amniocentesis criteria and confirmed by histopathologic features), persistent uterine activity accompanied by cervical change (consistent with the diagnose of preterm labour), or any other contraindication for a cerclage procedure.”
Interventions	McDonald cerclage (N = 31) versus no cerclage (N = 30) All prospective participants had indomethacin and clindamycin before randomisation. Women in the cerclage group had indomethacin and clindamycin for 24 h after the cerclage procedure, while women in the no cerclage group had indomethacin and clindamycin stopped at 24 h after randomisation. Women were send home after 24 h and monitored weekly by ultrasound
Outcomes	Perinatal death, neonatal morbidity according to 4 categories: none (routine neonatal care), minimal (intensive care admission with no mechanical ventilation or serious morbidity), serious (mechanical ventilation, respiratory distress syndrome, necrotizing enterocolitis, intraventricular haemorrhage, sepsis, or other life‐threatening morbidity), and perinatal death (stillborn fetus or death during the first 28 days after birth)
Notes	Additional information and the data base for cross‐checking of the published results provided by the first author
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	“If the patients continued to meet inclusion criteria, they were randomly assigned to receive a McDonald cerclage under regional anaesthesia or not cerclage therapy.”
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding of participants and personnel (performance bias) All outcomes	High risk	Impossible to blind to participants and personnel
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not stated if the outcome assessors were blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Loss of participants:   135 patients met the inclusion criteria; 20/135 declined randomisation.  Exclusion of participants after randomisation: 2/135 were excluded because of chorioamnionitis that was diagnosed by amniocentesis. Intention‐to‐treat analysis: “A rescue arm of the study was designed for each group. Any patient at < 24 weeks' gestation who had prolapsed membranes beyond the level of the cerclage or to the external os (without cerclage) was offered a revision or rescue cerclage procedure. Data were analysed on the basis of intention to treat”.
Selective reporting (reporting bias)	Low risk	Study protocol not available. The full database was provided by the authors, so any selective reporting unlikely
Other bias	Low risk	Study was not stopped early. No apparent baseline imbalance