Althuisius 2001.

Methods	RCT ‐ block randomisation. July 1995 to July 2000. University Hospital Vrije Universiteit and Olze Lieve Vrouwe Gastus, Amsterdam
Participants	Eligible participants from 3 populations: Group I: “Women with a previous PTL before 34 weeks of gestation who met clinical criteria for the diagnosis of cervical incompetence or previous PPROM before 32 weeks were allocated to receive a prophylactic cerclage or not in a proportion of 1:2” “TV US follow‐up examination of the cervix was performed in both groups. When a patient of the group without prophylactic cerclage had a cervical length of < 25 mm before 27 weeks, a secondary randomisation was performed that allocated women for treatment with therapeutic cerclage with bed rest vs bed rest only”. Group II: “Women with a gynaecological history with one or more accepted risk factors for cervical incompetence, such as cold knife conization, exposure to diethylstilbestrol in utero, and uterine anomaly, were followed by TV US of the cervix; and when a cervical length of < 25 mm was found before 27 weeks of gestation, randomisation allocated women to therapeutic cerclage and bed rest vs bed rest only”. In both the first and second groups, women were included before a GA of 15 weeks. Group III: "Women who met the inclusion criteria of I and II group but who had a gestational age of > 15 weeks with a cervical length of < 25 mm before 27 weeks of gestation or women who had symptoms of cervical incompetence, such as the feeling of pressure low in the abdomen and mucous vaginal discharge and a cervical length of < 25 mm before 27 weeks, were randomised to receive therapeutic cerclage and bed rest vs bed rest only”. Women randomised and included in this review came from groups I ( N = 18), II (N = 8) and III (N = I0) Inclusion criteria:  “high risk of PTL as diagnosed by cervical length of < 25 mm before gestational age of 27 weeks.” “…cervical length was measured by TV US in women with risk factors or symptoms of cervical incompetence” “only patients with singleton pregnancies were included”. Exclusion criteria: women with pregnancies complicated by fetal congenital/chromosomal anomalies, PROM, membranes bulging into the vagina, or intrauterine infection in the current pregnancy were not eligible for trial entry
Interventions	Therapeutic cerclage (N = 20) with bed rest compared to bed rest only (N = 16). One woman was excluded due to bulging membranes, leaving 19 women in the cerclage group
Outcomes	Primary: PTL < 34 weeks, neonatal morbidity defined as admission to NICU and/or neonatal death and neonatal survival. Secondary: not stated
Notes	Additional information and the database for cross‐checking of the published results provided by the first author
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Random allocation was stratified for the different inclusion criteria and the 2 participating hospitals and organised in balanced blocks. It is not stated how was the random sequence generated
Allocation concealment (selection bias)	Low risk	Telephone randomisation
Blinding of participants and personnel (performance bias) All outcomes	High risk	Impossible to blind for participants and clinicians
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not stated if outcome assessors were blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Any loss of participants to follow‐up at each data collection point:      3 lost to follow‐up. Any exclusion of participants after randomisation: 1 patient was excluded because the membrane was bulging into the vagina. Intention‐to‐treat analysis
Selective reporting (reporting bias)	Low risk	Full study protocol not available, but prespecified data extraction form provided by authors.    Secondary outcome not prespecified in the article
Other bias	Low risk	Study was not stopped early. No baseline imbalance