A number of implementation challenges exist for micronutrient supplementation. Access to care is often associated with socioeconomic status and may influence women's access to and use of supplementation programs. For instance, in one study, the highest wealth quintile of pregnant women had the highest use of iron and folic acid supplementation during antenatal care (33). However, even for women who have access to micronutrient supplements, the coverage and quality of micronutrient supplementation programs were limited (39). Incorrect doses, inadequate supplies, and incomplete adherence were major limitations (33), and poorly performing programs had limited impact on nutrition outcomes (59). Integration of supplementation programs with behavior change interventions improved knowledge, adherence, and coverage of supplementation interventions (32, 33, 60). The use of local micronutrient-rich foods can also help overcome limitations associated with supplement provision. In Nepal, improvements in the dark adaptation of night-blind pregnant women did not differ significantly between food and synthetic sources of vitamin A (61). When available, consumption of micronutrient-rich foods can be as effective as micronutrient supplements.

Our findings identified gaps and limitations in the evaluation, scope, targeting, and delivery platforms of nutrition interventions in low- and middle-income countries. First, the monitoring and evaluation of nutrition programs that reported on women's nutrition outcomes was generally inadequate. Many of the studies we identified included small-scale efficacy trials. Although there were many large-scale programs that targeted women and adolescent girls with nutrition-specific and nutrition-sensitive approaches, they lacked rigorous evaluation. Whether the evidence about women's outcomes was limited because they are not systematically measured or because they are not well reported is not clear. Negative results are often not published, and many evaluations of nutrition interventions that are conducted by the same groups responsible for implementing them are typically presented positively. This may have also skewed our findings. More intentional research-quality program evaluation, including of large-scale programs, would provide a stronger evidence base. Of the studies identified in this review, many reported on short-term findings such as changes in knowledge, dietary behaviors, and program coverage. They were limited in their ability to report clinical and anthropometric outcomes for women, the duration of those outcomes, and the feasibility of scaling up programs. There is also a need for systematic, long-term evaluations of interventions whose effects on nutrition outcomes are more distal (e.g., nutrition education compared with micronutrient supplementation). The effects of multisectoral interventions are even more complex to measure. However, frameworks exist to evaluate complex interventions (102) and could be utilized to evaluate the impact of interventions across the life course.