Birth before 37 weeks
The association between technique of cervical cerclage and the primary outcome of birth less than 37 weeks is shown in Figure 2. Twelve studies (70.5%) reported data on this outcome. There were significantly lower rates of birth before 37 weeks in the Shirodkar group when compared to the McDonald group (RR 0.91, 95% CI 0.85-0.98).
Removing studies with serious risk of bias improved the quality of evidence from low to moderate and did not alter the results. No subgroup analysis was undertaken.