Abstract: This updated review includes a total of 15 trials (3490 women); three trials were added for this update (152 women). Cerclage versus no cerclage Overall, cerclage probably leads to a reduced risk of perinatal death when compared with no cerclage, although the confidence interval (CI) crosses the line of no effect (RR 0.82, 95% CI 0.65 to 1.04; 10 studies, 2927 women; moderate quality evidence). Considering stillbirths and neonatal deaths separately reduced the numbers of events and sample size. Although the relative effect of cerclage is similar, estimates were less reliable with fewer data and assessed as of low quality (stillbirths RR 0.89, 95% CI 0.45 to 1.75; 5 studies, 1803 women; low quality evidence; neonatal deaths before discharge RR 0.85, 95% CI 0.53 to 1.39; 6 studies, 1714 women; low quality evidence). Serious neonatal morbidity was similar with and without cerclage (RR 0.80, 95% CI 0.55 to 1.18; 6 studies, 883 women; low-quality evidence). Pregnant women with and without cerclage were equally likely to have a baby discharged home healthy (RR 1.02, 95% CI 0.97 to 1.06; 4 studies, 657 women; moderate quality evidence). Pregnant women with cerclage were less likely to have preterm births compared to controls before 37, 34 (average RR 0.77, 95% CI 0.66 to 0.89; 9 studies, 2415 women; high quality evidence) and 28 completed weeks of gestation. Five subgroups based on clinical indication provided data for analysis (history-indicated; short cervix based on one-off ultrasound in high risk women; short cervix found by serial scans in high risk women; physical exam-indicated; and short cervix found on scan in low risk or mixed populations). There were too few trials in these clinical subgroups to make meaningful conclusions and no evidence of differential effects. Cerclage versus progesterone Two trials (129 women) compared cerclage to prevention with vaginal progesterone in high risk women with short cervix on ultrasound; these trials were too small to detect reliable, clinically important differences for any review outcome. One included trial compared cerclage with intramuscular progesterone (75 women) which lacked power to detect group differences. History indicated cerclage versus ultrasound indicated cerclage Evidence from two trials (344 women) was too limited to establish differences for clinically important outcomes. Cervical cerclage reduces the risk of preterm birth in women at high-risk of preterm birth and probably reduces risk of perinatal deaths. There was no evidence of any differential effect of cerclage based on previous obstetric history or short cervix indications, but data were limited for all clinical groups. The question of whether cerclage is more or less effective than other preventative treatments, particularly vaginal progesterone, remains unanswered.

Plain-language summary: We searched for evidence up to 30 June 2016. This review includes 15 studies involving 3490 women (3 studies involving 152 women were added for this update). Women with a stitch are less likely to have a baby who is born too early. Babies whose mothers had a stitch are also less likely to die during the first week of life. It is not clear whether a cervical stitch can prevent stillbirth or improve the baby's health once born. Inserting a stitch helps pregnant women who are at high risk avoid early births compared to no stitch. Inserting a stitch may also improve a baby's chance for survival. We found too few clinical trials to understand whether cervical stitch is more effective than other treatments for preventing early births, such as progesterone (a hormone drug used to prevent early birth). We found too few data to understand if it is better to have a stitch inserted early in pregnancy (based on the mother's previous history) or to wait to perform an ultrasound scan later in pregnancy to see if the cervix has become shortened.