INTRODUCTION: Electronic decision-support systems (EDSSs) aim to improve the quality of antenatal care (ANC) through adherence to evidence-based guidelines. We assessed the potential of the mHealth integrated model of hypertension, diabetes, and ANC EDSS and the World Health Organization EDSS to improve the quality of ANC in primary-level health care facilities in Nepal. METHODS: From December 2021 to January 2023, we conducted a mixed-methods evaluation in 19 primary-level ANC facilities in Bagmati Province, Nepal. Implementation was from March 2022 to August 2022. We conducted a health facility survey, ANC clinical observations, longitudinal case studies and validation workshop, in-depth interviews, monitoring visits, research team debriefing meetings, health care provider attitude survey, and stakeholder engagement and feedback meetings. Results were integrated using concurrent triangulation to develop explanations about the EDSS implementation process and the effects observed. RESULTS: We identified 9 themes on implementation challenges that hindered the EDSS from generating the desired improvements to ANC quality. Facility readiness and provider confidence in using the EDSS were mixed. It was not always used or used as intended, and the approach to ANC provision did not change. EDSS inflexibility did not reflect how staff made decisions about pregnant women's needs or ensure that tests were done at the right time. There was mixed evidence that ANC staff believed that the EDSS benefited their work. The EDSS did not become fully integrated into existing health systems. Engagement of essential stakeholders fell short. CONCLUSION: Different understandings of and inconsistent use of the EDSS highlighted the need for increased training and support periods, greater stakeholder engagement, and further integration into existing health systems. Our novel approach to integrating findings from multiple substudies offers uniquely valuable insights into the many factors needed for the successful implementation of an EDSS to improve the quality of ANC in Nepal.