Effects of a social network modification of a community-based family planning intervention on contraceptive use among adolescent wives in Niger: a cluster randomized controlled trial

Niger has the worlds highest adolescent fertility rate. Social network (SN) approaches to family planning may improve intervention impact through diffusion beyond direct beneficiaries. We tested a social network modification of a community-based family planning intervention to increase contraceptive use compared to standard implementation and control.Three-arm cluster-randomized trial in 56 rural villages in Maradi, Niger. Eligible participants were adolescent wives (AW) aged 15-19 with 0-1 children and their husbands. Villages were randomized using covariate-constrained randomization (Minirand): standard Kulawa (100% coverage), SN modification (50% coverage pairing AW-mother-in-law dyads with adopt-a-friend diffusion), or control. Interventions were delivered over 12 months. Blinding of participants and implementers was infeasible; analysts were blinded. Primary outcome was current contraceptive use assessed at endline and analyzed using intention-to-treat difference-in-differences logistic regression adjusting for clustering; no missing data were imputed. ClinicalTrials.gov NCT05777473; trial closed to enrollment.From May 1 to September 30, 2022, 1,538 female AW were enrolled (517 control, 532 Kulawa, 489 Kulawa SN); 1,396 (90.8%) completed endline (May-August 2024). Compared to control, the SN arm significantly increased contraceptive use (AOR 2.36, 95% CI 1.27-4.44); the standard arm showed no significant effect (AOR 1.36, 95% CI 0.76-2.41). Within SN villages, both non-participants (AOR 2.66, 95% CI 1.25-5.70) and direct participants (AOR 2.10, 95% CI 0.99-4.44) showed increased use versus control, demonstrating behavioral diffusion. No intervention-related adverse events were observed in any arm. An SN approach targeting AWs, husbands, mothers-in-law, and adopted friends achieved greater effects than standard implementation despite 50% lower coverage, with evidence of diffusion to non-participants. Leveraging social networks may improve impact of family planning programs in high-fertility settings.