Simcox 2009.

Methods	RCT. November 2003 to March 2006. 9 UK hospitals
Participants	Participants (N = 248):  pregnant women < 24 weeks of gestation. Inclusion criteria: singleton pregnancy with at least 1 previous spontaneous delivery between 16 + 0 and 34 + 0 weeks. Exclusion criteria: unable to give informed consent
Interventions	Cerclage based on history “For those women allocated to the history‐indicated arm of the trial, a history‐indicated suture was offered if the treating clinicians considered that the obstetric history justified a cerclage. There were no prescribed minimum criteria for history‐indicated suture insertion. The decision to insert a cerclage or not, based on history, was made in every case before randomisation by the attending clinician, and then carried out if the patient was randomised to history arm” versus Cerclage based on serial US scanning “Women allocated to the scanning arm of the trial underwent cervical length assessment by transvaginal US every 2 weeks from entry into the trial until 24 + 0 weeks of gestation. If the cervix shortened to ≤ 20 mm, a cervical cerclage was inserted.”
Outcomes	Primary: PTD before 34 weeks. Secondary: frequency of suture insertion, incidence of histological chorioamnionitis, incidence of maternal pyrexia, hospital admissions, bed rest, use of steroids, tocolysis and progesterone. Neonatal outcomes: need for oxygen therapy at 28 days and US evidence of brain abnormality
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	“The randomisation sequence was computer generated in balanced block multiples. Stratification was performed to control for gestation of last delivery before 24 weeks.”
Allocation concealment (selection bias)	Low risk	"Allocation was made by telephone to the central trials office in London, UK.”
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 to follow‐up: “primary outcome data were available on 247/248 women (99.6%)”.                                                   Exclusion of participants after randomisation: 5 women were excluded “three were subsequently identified as not fitting eligibility criteria and a further two were excluded from analysis as they elected to terminate the pregnancy after a diagnosis of fetal anomaly”. Intention‐to‐treat analysis: “There were 9 patients who did not receive the randomisation intervention. Eight women in the history arm were scanned” “All analysis was conducted according to the original allocation, following the intention to treat principle."
Selective reporting (reporting bias)	Unclear risk	Study protocol not available. All outcomes prespecified in the article were reported
Other bias	Low risk	Study was not stopped early Baseline imbalance: “One women in each arm declined a suture.”