Objective: The MAMAACT intervention aims to reduce ethnic and social disparities in stillbirth and infant death by improving communication between pregnant women and midwives regarding warning signs of pregnancy complications. This study evaluates the effect of the intervention on pregnant women's health literacy (two domains from the Health Literacy Questionnaire) and complication management — interpreted as improved health literacy responsiveness among midwives. Design: Cluster randomized controlled trial, 2018–2019. Setting: 19 of 20 Danish maternity wards. Participants: Cross-sectional survey data were collected using telephone interviews (n = 4150 pregnant women including 670 women with a non-Western immigrant background). Intervention: A six-hour training session for midwives in intercultural communication and cultural competence, two follow-up dialog meetings, and health education materials for pregnant women on warning signs of pregnancy complications — in six languages. Main outcome measures: Differences in mean scores at post-implementation of the domains Active engagement with healthcare providers (Active engagement) and Navigating the healthcare system from the Health Literacy Questionnaire, and differences in the certainty of how to respond to pregnancy complication signs between women in the intervention and control group. Results: No difference was observed in women's level of Active engagement or Navigating the healthcare system. Women from the intervention group were more certain of how to respond to complication signs: Redness, swelling, and heat in one leg: 69.4 % vs 59.1 %; aOR 1.57 (95 % CI 1.32–1.88), Severe headache: 75.6 % vs 67.3 %; aOR 1.50 (95 % CI 1.24–1.82), and Vaginal bleeding: 97.3 % vs 95.1 %; aOR 1.67 (95 % CI 1.04–2.66). Conclusion: The intervention improved women's certainty of how to respond to complication signs, but was unable to improve pregnant women's health literacy levels of Active engagement and Navigating the healthcare system, likely due to barriers related to the organization of antenatal care. A reorganization of antenatal care and a care model sensitive to diversity within the entire healthcare system might help reduce disparities in perinatal health. Trial registration: ClinicalTrials.gov identifier: NCT03751774.