Sociodemographic characteristics associated with cervical cancer screening participation by send-to-all and opt-in HPV self-sampling: Who benefits? Results from a randomized controlled trial among long-term non-attending women in Norway

With the objective to investigate associations between sociodemographic characteristics and participation in interventions designed to increase participation in cervical cancer screening among under-screened women, we randomized a random sample of 6000 women in Norway aged 35-69 years who had not attended cervical screening for >= 10 years to receive either (i) a reminder to attend regular screening (control), (ii) an offer to order a self-sampling kit (opt-in), or (iii) a self-sampling kit unsolicited (send-to-all). We analyzed how sociodemographic characteristics were associated with screening participation within and between screening arms. In the send-to-all arm, increased screening participation ranged from 17.1% (95% confidence interval [95% CI] = 10.3% to 23.8%) to 30.0% (95% CI = 21.5% to 38.6%) between sociodemographic groups. In the opt-in arm, we observed smaller, and at times, non-significant increases within the range 0.7% (95% CI = -5.8% to 7.3%) to 19.1% (95% CI = 11.6% to 26.7%). In send-to-all versus control comparisons, there was greater increase in participation for women in the workforce versus not (6.1%, 95% CI = 1.6% to 10.6%), with higher versus lower income (7.6%, 95% CI = 2.2% to 13.1%), and with university versus primary education (8.5%, 95% CI = 2.4% to 14.6%). In opt-in versus control comparisons, there was greater increase in participation for women in the workforce versus not (4.6%, 95% CI = 0.7% to 8.5%), with higher versus lower income (6.3%, 95% CI = 1.5% to 11.1%), but lower increase for Eastern European versus Norwegian background (-12.7%, 95% CI = -19.7% to -5.7%). Self-sampling increased cervical screening participation across all sociodemographic levels, but inequalities in participation should be considered when introducing self-sampling, especially with the goal to reach long-term non-attending women.