Building a National Lens on Severe Adverse Maternal Events in Pregnancy: The Case for CanOSS

A nationwide survey of Canada’s birthing units has found strong support for creating a coordinated system to review serious complications in pregnancy, birth, and the postpartum period. Nearly 60 per cent of the 289 birthing units across the country took part in the study, and three-quarters indicated they would be willing to contribute anonymised data on severe adverse maternal events in pregnancy to a central system. Published in Public Health in Practice, the findings confirm that Canada is ready to establish the Canadian Obstetric Survey System (CanOSS).
The survey shows that most birthing facilities already review severe adverse maternal events locally, but these reviews are fragmented. Facilities rely on different terms to describe these events, from “serious adverse pregnancy outcome” to “severe maternal morbidity” and “critical incident.” Although each facility has its own rationale for which conditions to review, there is no consistency across units in terms of which conditions are reviewed or at what severity.
Variation in local review practices further underlines the case. While 80 per cent of units reported reviewing severe maternal morbidity, the composition of teams and the way reviews are conducted varied widely. Anaesthesia, midwifery, internal medicine, and critical care – specialities central to the management of severe adverse maternal events – were often missing from the discussion. Findings were also almost never shared beyond the hospital in which the event occurred. This highlights a missed opportunity to act on lessons and recommendations and to prevent these conditions in other facilities.
“Canada has the building blocks – local reviews, dedicated teams, and willingness to share – but without a shared framework, comparisons are difficult and patterns remain obscured,” says Rizwana Ashraf, co-author of the study. “CanOSS would provide the structure needed to connect insights and reduce preventable harm.”
The survey findings reinforce this point. Postpartum haemorrhage, hypertensive disorders, and infections emerged as the leading causes of severe adverse maternal events across Canadian units. Each of these conditions has clear evidence-based guidelines for prevention and management, yet they remain the most common contributors to morbidity. Their persistence highlights that identifying problems is not enough; a system is needed to ensure learning translates into consistent action.
“The incidence of severe adverse maternal events is increasing in Canada. By examining not just outcomes but the pathways that lead to them, CanOSS can help identify preventable factors and guide improvements in care. The feasibility has now been demonstrated – our responsibility is to act on it,” says Rohan D’Souza, senior author of the study and Associate Professor in the Departments of Obstetrics & Gynecology and Health Research Methods, Evidence, and Impact at McMaster University.
He adds: “This work is about turning local knowledge into collective learning, so that no facility has to face these challenges in isolation.”
The survey also drew attention to equity. Smaller and rural hospitals were less likely to respond, in part because severe cases are often transferred to higher-acuity centres. Yet their experiences remain vital to building a complete national picture. Ensuring their inclusion will be central to the development of CanOSS.
“This work demonstrates that a concerted effort to build collective learnings is possible and that individual birthing units have the willingness and capacity to join such a grassroots initiative. In thinking about severe adverse events as the result of multiple contributing factors and adopting a framework aimed at going ‘beyond the numbers’, the CanOSS approach can be a catalyst for improvements in pregnancy and post-pregnancy care,” says Dr. Isabelle Malhamé, Associate Professor at Université de Montréal and Obstetric Medicine Physician at the Centre hospitalier Universitaire Sainte-Justine.
Taken together, the findings make clear that Canada has the infrastructure, commitment, and willingness to establish CanOSS. Moving from feasibility to implementation will ensure that lessons and recommendations emerging from severe adverse maternal events reviews no longer remain within individual birthing facilities but are reviewed confidentially and respectfully by an external panel of multidisciplinary experts and shared nationally – and internationally – helping to strengthen care and improve pregnancy outcomes.