Background: WHO guidelines recommend integrating calcium supplementation into antenatal care (ANC) alongside iron and folic acid (IFA) to reduce maternal mortality. However, supplementation programs face multiple barriers, and strategies to improve adherence are needed. An adherence partner is someone whom pregnant women ask to support adherence at home.

Objectives: This study 1) assessed adherence partner acceptability, feasibility, and associations with calcium and IFA supplement adherence and 2) examined relations between social support and adherence.

Methods: This secondary analysis is from a trial integrating calcium supplementation into ANC in Kenya. ANC providers were trained on calcium and IFA supplementation and counseling, provided with behavior change materials, and given adequate supplement supplies. Pregnant women from 16 government health facilities were recruited (n = 1036); sociodemographic and adherence data were collected at baseline and at 4- to 6-wk follow-up visits. Adherence was measured with pill counts and self-reports. Culturally adapted scales measured social support in general and specific to adherence. Mixed-effects regression analyses were used to examine factors associated with adherence partners, social support, and adherence.

Results: Most participants received information about adherence partners (91%) and had a partner at follow-up (89%). Participants with adherence partners reported higher adherence support (OR: 2.10; 95% CI: 1.32, 3.34). Mean ± SD adherence was high for calcium (88.3% ± 20.7%) and IFA (86.1% ± 20.9%). Adherence support was positively associated with calcium adherence at follow-up by using pill counts (OR: 2.2; 95% CI: 1.1, 2.6) and self-report data (OR: 1.9; 95% CI: 1.2, 2.9), but there was not a direct relation between adherence partners and adherence.

Conclusions: Adherence support enhanced adherence to calcium supplements. The adherence partner strategy was highly acceptable and feasible but warrants further study. This research demonstrates the importance of adherence support and suggests that interventions to increase household-level support for antenatal micronutrient supplementation may be needed to implement the WHO guidelines.