OBJECTIVE: Gestational diabetes mellitus is a pregnancy-related complication and therefore obstetricians counsel and manage the maternal health care for these women. This study describes obstetricians' experiences of management of pregnant women with gestational diabetes mellitus. DESIGN: Interview study. SETTING: Hospital-based specialist maternal health care clinics in Sweden. POPULATION: A consecutive purposive national sample of 17 obstetricians providing maternal health care to pregnant women diagnosed with gestational diabetes mellitus. METHODS: Interviews were recorded and transcribed. The data were analyzed using qualitative content analysis. RESULT: The overall theme describing the experiences of the obstetricians was labeled 'Dealing with ambiguity'. This ambiguity permeated all aspects of working as an obstetrician within the maternal health care; the role of the obstetrician, the context of organization, the multifaceted maternal and fetal interests to balance, and lack of consensus, recommendations and evidence-based knowledge. CONCLUSIONS: The study revealed the ambiguous situation experienced and managed by obstetricians providing maternal health care to pregnant women diagnosed with gestational diabetes mellitus. This indicates a need for national guidelines and standardized maternal health care services regarding gestational diabetes mellitus to fulfill the intentions of the health care system. Such recommendations may be beneficial and supportive for the health care professionals as well as for the mother-to-be and her fetus.