Objectives To explore how low-income pregnant women use Healthy Start food vouchers, the potential impacts of the programme, and which women might experience these impacts and why.

Design A realist review.

Eligibility criteria for selecting studies Primary or empirical studies (of any design) were included if they contributed relevant evidence or insights about how low-income women use food vouchers from the Healthy Start (UK) or the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) programmes. The assessment of ‘relevance’ was deliberately broad to ensure that reviewers remained open to new ideas from a variety of sources of evidence.

Analysis A combination of evidence synthesis and realist analysis techniques was used to modify, refine and substantiate programme theories, which were constructed as explanatory ‘context–mechanism–outcome’–configurations.

Results 38 primary studies were included in this review: four studies on Healthy Start and 34 studies on WIC. Two main outcome strands were identified: dietary improvements (intended) and financial assistance (unintended). Three evidence-informed programme theories were proposed to explain how aspects of context (and mechanisms) may generate these outcomes: the ‘relative value’ of healthy eating (prioritisation of resources); retailer discretion (pressure to ‘bend the rules’); the influence of other family members (disempowerment).

Conclusions This realist review suggests that some low-income pregnant women may use Healthy Start vouchers to increase their consumption of fruits and vegetables and plain cow’s milk, whereas others may use them to reduce food expenditure and save money for other things.