Background
Transvaginal ultrasound measurement of cervical length is useful after suture insertion in predicting preterm delivery. However, there is little evidence to guide practice in the clinical scenario when fetal membranes are seen on ultrasound to be prolapsing distal to a cervical suture.

Aim
To determine whether a reinforcing cerclage reduced preterm delivery in those women with ultrasound evidence of fetal membranes prolapsing distal to the first suture.

Methods
A retrospective cohort study was conducted on women with a cervical suture in situ plus ultrasound evidence of fetal membranes prolapsing through the first suture. Exposed patients were those managed with a reinforcing cerclage. The unexposed group were women who were managed expectantly, without a reinforcing cerclage.

Results
Those women with a reinforcing cerclage were significantly more likely to deliver at an earlier gestation compared with those managed expectantly: 26+0 (±5+1) compared with 31+1 (±7+0) weeks, P = 0.047. More women in the reinforcing cerclage group delivered at <32 completed weeks' gestation: 12/13 (92%) versus 5/12 (42%), P = 0.01. There was no significant difference in the rate of second‐trimester miscarriages between the expectant management group and those with a reinforcing cerclage: 2/12 (17%) versus 5/13 (38%), P = 0.38. Conclusion Our study found that a reinforcing cerclage following primary cerclage failure hastened preterm delivery. The role of transvaginal ultrasound measurement of cervical length postsuture is debatable if the possible intervention is not beneficial and may be detrimental.