Objective: To elucidate the mechanisms by which a cash incentive intervention increases retention in prevention of mother-to-child transmission services.
Methods: We used data from a randomized controlled trial in Kinshasa, Democratic Republic of Congo. Perceptual factors associated with loss to follow-up (LTFU) through 6 weeks postpartum were first identified. Then, binomial models were used to assess interactions between LTFU and identified factors, and the cash incentive intervention.
Results: Participants were less likely to be LTFU if they perceived HIV as a "very serious" health problem for their baby vs. not [risk difference (RD), -0.13; 95% confidence interval (CI): -0.30 to 0.04], if they believed it would be "very likely" to pass HIV to their baby if they did not take any HIV drug vs. not (RD, -0.15; 95% CI: -0.32 to 0.02), and if they anticipated that not having money would make it difficult for them to come to the clinic vs. not (RD, 0.12; 95% CI: -0.07 to 0.30). The effect of each of the 3 factors on LTFU was antagonistic to that of receiving the cash incentive intervention. The excess risk due to interaction between the cash incentive intervention and the anticipated difficulty of "not having money" to come to the clinic was exactly equal to the effect of removing this perceived barrier (excess risk due to interaction, -0.12; 95% CI: -0.35 to 0.10).
Conclusions: Our analyses show that cash transfers improve retention in prevention of mother-to-child transmission services mainly by mitigating the negative effect of not having money to come to the clinic.