Lazar 1984.

Methods	RCT Dates of data collection: not stated. Setting: 4 obstetric teams used cervical cerclage for “obvious cervical incompetence”; an initial partial score was established at the first visit, and then recalculated at each visit between 10 and 28 weeks' gestation; hospitals in France
Participants	N = 506 (268 cerclage, 238 no cerclage) Inclusion criteria “The eligibility of the rest was assessed using a scoring system." The scores were established by points given to two kinds of risk factors: ”permanent” (factors present before the index pregnancy) and “evolving” (factors that appeared or changed during the pregnancy).” “Patients with score ≥ 20 points at the first visit were deemed to be ineligible for the trial. Similarly, low risk patients with scores < 9 at the first or subsequent visits were also deemed to be ineligible. Women became eligible for the entry into the trial as soon as a score of ≥ 9 had been reached, and they remained in the trial whether or not the score subsequently rose to ≥ 20. The target trial population were pregnant women who had a risk of cervical incompetence that was lower than the pregnant women excluded for the following" Exclusion criteria Previous late spontaneous abortion of a living fetus at 14 to 28 weeks. State of the cervix (cervix torn up to the lateral cul de sac; cervix open including inner os (1 finger width). Enlargement of uterine isthmus ≥ 1 cm in width demonstrated at hysterogram. Twin pregnancies
Interventions	Cerclage versus no cerclage
Outcomes	Not specified
Notes	242/268 women in cerclage arm received cerclage; 26 women in no cerclage arm had cerclage
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	“…eligible patients were randomly allocated (using prepared envelopes) into…”
Allocation concealment (selection bias)	Unclear risk	“…eligible patients were randomly allocated (using prepared envelopes) into…”
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	Unclear risk	Losses to follow up not reported.                                                   Exclusion of participants after randomisation not reported. Analysis appears to be intention‐to‐treat “Of the women entered into the trial, 90% received the management to which they had been allocated.”
Selective reporting (reporting bias)	Unclear risk	Study protocol not available
Other bias	High risk	Study stopped early: “It was decided to conduct a first analysis of the data after about 500 patients had been recruited, and to decide in the light of the results whether or not to pursue the trial. The results reported here are those of the first analysis.” Baseline imbalance: “Women allocated to the cerclage policy, however, were more likely to have had previous abortions. This difference is largely a reflection of a difference between the experimental and control groups in one of the four centres. Although selection bias may have been operating in this centre we have included data derived from cases and controls managed there because analyses conducted after excluding these patients did not make any difference to the conclusions we have reached after analysing data derived from all four centres.”