Maternal health across Papua New Guinea (PNG) is of extreme public health concern. In response, the National Department of Health explicitly prioritized improving maternal, neonatal and child health services, envisaging increased collaboration between the formal health system and community-based initiatives as one method for achieving this. This study examined the patterns of formal and non-formal service utilization during pregnancy and childbirth in one province. We analysed the activity database of the East Sepik Women and Children's Health Project's Village Health Volunteer (VHV) program, an informal health service in East Sepik Province of PNG, estimating VHV activity and coverage for two maternal health care services (first antenatal care visit and VHV-attended deliveries) and comparing these to the volume and estimated coverage of these services delivered by the formal health system in East Sepik over the years 2007 to 2010. We found a significant increase in women's utilization of VHVs for first antenatal care and for an attended delivery. Reported coverage of these services delivered by the formal health service declined or at best remained static over the same time period. Our data cannot illuminate the causes of an apparent and highly concerning decline in health facility usage for assisted delivery, nor the reasons for increased usage of VHVs. The factors contributing to these trends in service provision require urgent study, to improve our understanding of the drivers of utilization of critical maternal health services. Our study demonstrates that VHVs deliver a substantial proportion of maternal health services in East Sepik. This finding alone highlights the importance of considering this cadre when planning health service improvements and suggests that a national VHV policy that builds on the work of the National Health Plan in defining the most appropriate role for VHVs in maternal health care is long overdue.