Methods	Randomised controlled trial of routine antepartum care versus routine antepartum care plus a preterm birth prevention clinic in which symptoms and signs of labour were taught and the cervix examined at weekly visits between 20 and 36 weeks’ gestation
Participants	370 pregnant women considered high risk for preterm birth based on use of the Creasey Scoring system (Creasy 1980). Women were selected from 2829 women attending prenatal clinic at the Department of Obstetrics and Gynecology, Ohio State University, Ohio
Interventions	Preterm birth prevention clinic in which symptoms and signs of labour were taught and the cervix examined at weekly visits between 20 and 36 weeks’ gestation
Outcomes	Preterm labour diagnosed before 37 weeks’ gestation when cervical changes accompanied persistent uterine contractions despite bedrest and intravenous hydration, or, if the cervix was already 2 cm dilated and/or 50% effaced, when 8 contractions/hour persisted despite bedrest and parenteral hydration
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient information about the sequence generation process to permit judgement of risk of bias
Allocation concealment (selection bias)	Unclear risk	Insufficient information about the sequence generation process to permit judgement of risk of bias
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Insufficient information about the sequence generation process to permit judgement of risk of bias
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No reporting of attrition or exclusions.
Selective reporting (reporting bias)	Unclear risk	Insufficient information about the sequence generation process to permit judgement of risk of bias.
Other bias	Unclear risk	Does not explicitly state that only singleton pregnancies were included in the study. No comment is made on what cut-off was used for the Creasy scoring system to define women as of high risk of preterm birth (Creasy 1980).