Gordon 2006

Methods	RCT.
Participants	Twin gestations; asymptomatic and with PTL symptoms; 15 to 34 weeks. N = 125.
Interventions	TVU CL screening at 15 to 28 weeks, and if PTL symptoms develop or not (the control group did not receive TVU CL). Time TVU CL results available: not specified. Protocol for TVU knowledge group: yes.
Outcomes	Primary: length of gestation.
Notes	Only abstract published; unclear if intention‐to‐treat; only twins; protocol for management of TVU CL group. Short TVU CL not available.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomization not described.
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Different protocols for study and control groups.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Primary outcome objective ‐ length of gestation.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No incomplete outcomes mentioned.
Selective reporting (reporting bias)	Unclear risk	Primary outcome was gestational age at delivery.
Other bias	Unclear risk	Abstract only, so data reported are limited.