This article concerns knowledge negotiations as an aspect of interactional power in three-way interaction between Arabic-speaking women, Swedish-speaking midwives and interpreters in Swedish antenatal care. The notion of epistemic stance is used to investigate how all three participants negotiate knowledge, and how this affects the ongoing consultation. The data consist of audio recordings of 33 consultations, involving five midwives. Using an interaction analytical approach, the study focuses on sequences where the pregnant woman makes her voice heard, possibly challenging the midwife or the Swedish antenatal care programme. Three different ways in which the epistemic stances of the participants unfold interactionally are analysed: (1) the midwife and the pregnant woman mutually adjusting their knowledge claims, (2) the pregnant woman unsuccessfully attempting to claim knowledge and (3) participants jointly asserting the midwife's knowledge. Importantly, all three participants wield their interactional power through various ways of negotiating knowledge, which contrasts with the idea of the interpreter as fully neutral and detached. The knowledge claims of the pregnant women and the midwives in the data are also shown to be highly dependent on the interpreters' competence and performance.