Recruiting to Clinical Trials on the Telephone - a randomized controlled trial

Informed consent is an essential element of clinical research. Obtaining consent, however, may be challenging. The use of the telephone for giving information and obtaining consent may be practical but little formal research has been done.

We examined the use of the telephone for the purpose of informing expectant mothers about The Danish Calmette Study; a randomized clinical trial assessing neonatal Bacille Calmette-Guérin vaccination. Expectant mothers received an invitation letter with a Participant Information Sheet about The Danish Calmette Study, the present trial, and a Consent Form. Two to 4 weeks later we contacted the mothers to discuss potential participation in the present trial. At this initial telephone contact, and after consent from the mothers, we randomized expectant mothers to receive the verbal information about The Danish Calmette Study by telephone, or at a face-to-face consultation. The primary outcome was a communication score, consisting of comprehension of information about The Danish Calmette Study and satisfaction with the information process. The outcome was measured using a questionnaire 2 days after the information was provided, and 2.5 months after the birth of the child.

The communication score obtained 2 days after information was given was significantly reduced in the telephone group, effect size -0.74 (95% confidence interval (CI), -1.11 to -0.36). The effect sizes of the subscores were -0.87 (95% CI, -1.25 to -0.49) for satisfaction and -0.22 (95% CI, -0.58 to 0.14) for comprehension. The effect sizes were slightly reduced when assessed 2.5 months after the birth.

The communication score was reduced in the telephone group. This was due to a reduction in satisfaction, while no difference in the comprehension could be found in comparison to the control group. This may be ethically acceptable as both groups had high satisfaction scores.

ClinicalTrials.gov, registered on 5 October 2015 with trial registration number NCT02570061 .