Background: Interprofessional communication is a critical component of safe maternity care. The literature reports circumstances in Aotearoa New Zealand and overseas when interprofessional collaboration works well between midwives and obstetricians, as well as descriptions of unsatisfactory communication between the two professions. Aim: To explore and define effective collaboration between midwives and obstetricians at the primary/secondary interface in maternity care, in order to generate suggestions to foster positive collaboration. Method: Eight primary care midwives, three obstetricians and two obstetric registrars from a single District Health Board in Aotearoa New Zealand were interviewed about their interactions at the primary/secondary interface and their understanding, and use, of the Referral Guidelines. The theoretical perspective was Appreciative Inquiry. Data were analysed using thematic analysis. Findings: Results indicate usually positive interprofessional interactions. Dominant emergent themes are the need to negotiate differing philosophies, to clarify blurred boundaries that sometimes lead to lack of clear lines of responsibility, and the importance of three-way conversations. Of the three themes, this article focuses on three-way communication between midwife, obstetrician/registrar and woman. Participants reported that, when effective three-way communication between woman, midwife and obstetrician occurred, philosophical difference could be negotiated, blurred boundaries clarified and understanding of the respective roles of the LMC midwife and the obstetric team promoted. Participants value the Referral Guidelines but report some limitations to their applicability. Conclusion: Effective three-way communication promotes good maternity care. This study has identified ways to support optimal communication.