Cerclage suture type to prevent pregnancy loss in women requiring a vaginal cervical cerclage: the C-STICH RCT

Background: Second trimester miscarriage and preterm birth is a significant global problem. Surgical cervical cerclage is performed to prevent pregnancy loss and preterm birth. It utilises either a monofilament or braided suture. It is hypothesised that a braided material becomes colonised with pathogenic bacteria that causes vaginal dysbiosis, infection and cerclage failure. Objectives: The primary objective of the study was to examine the effectiveness of using a monofilament suture material as opposed to a braided suture material on pregnancy loss in women requiring a vaginal cervical cerclage. Design: Superiority open randomised controlled trial. Setting: Seventy-five maternity sites across the UK. Participants: Women experiencing a singleton pregnancy requiring a cervical cerclage. Interventions: Monofilament suture or braided suture. Main outcome measures: The primary outcome was pregnancy loss (miscarriage and perinatal mortality, including any stillbirth or neonatal death in the first week of life). Secondary outcomes included the core outcome set for preterm birth. Methods: Women were randomised on a 1 : 1 basis to monofilament or braided cerclage utilising a bespoke randomisation service with minimisation dependent on the site, indication for cerclage, intention to use progesterone and planned surgical technique. The inclusion criteria were three or more previous mid-trimester losses or preterm births, insertion of a cerclage in a previous pregnancy, a history of a mid-trimester loss or preterm birth with a shortened cervical length in the current pregnancy or in women who clinicians deemed at risk of preterm birth. The exclusion criteria were an emergency or rescue cerclage, age of < 18 years, being unable to give informed consent or the cerclage having to be placed abdominally. The original sample size was calculated based on a relative risk reduction of 41% from a pregnancy loss rate of 19% in the braided group to 11% in the monofilament group with 90% power and alpha at p = 0.05. The independent data monitoring committee noted a lower-than-anticipated pooled event rate within the trial and recommended an increase in sample size to 2050. The outcome data were collected using clinical record forms from the maternal and neonatal medical records and reported to Birmingham Clinical Trials Unit. Results: A total of 2049 women were randomised, after withdrawals and loss to follow-up, data on 1005 women in the monofilament group and 993 women in the braided group were included. The baseline demographics between the groups were similar. There was no evidence of a difference in pregnancy loss rates between the monofilament and braided groups (80/1003 vs. 75/993; adjusted risk ratio: 1.05, 95% confidence interval: 0.79 to 1.40; adjusted risk difference: 0.002, 95% confidence interval: -0.02 to 0.03). Limitations: The trial did not collect long-term paediatric outcomes. There were no safety concerns. Conclusions: There was no evidence of a difference in pregnancy loss between a monofilament suture and a braided suture.