Study	Reason for exclusion
Beigi 2005	Compared history‐indicated to ultrasound‐indicated cerclage.
Burwick 2011	Used Cervilenz, which is a plastic instrument to measure the vaginal part of the cervix. This is outside the scope of our review, which focuses on CL measured exclusively by TVU.
Kassanos 2001	Compared history‐indicated to ultrasound‐indicated cerclage.
Lorenz 1990	Control group was not 'no ultrasound' or 'no knowledge', but was manual digital cervical exam. Interestingly, the study group utilized transabdominal ultrasound.
Matijevic 2006	The TVU CL information was blinded and not used for management.
Owen 1999	TVU information was not used for clinical care and no data on outcomes were provided.
Shennan 2007	Compared history‐indicated to ultrasound‐indicated cerclage.
Van Dijken 1991	Control group was not 'no ultrasound' or 'no knowledge', but was manual digital cervical exam. Interestingly, the study group utilized transabdominal ‐ not TVU.

CL: cervical length TVU: transvaginal ultrasound