“Invaluable” study confirms blood thinners don’t prevent recurrent pregnancy complications

October 18, 2016

Two years ago, Dr. Marc Rodger thought he had settled the debate about the use of blood thinners in pregnant women at high risk of developing blood clots. His trial of 292 women in five countries – the largest of its kind – definitely showed that the practice was not effective.

However, despite publication in The Lancet with a glowing commentary, some colleagues still didn’t want to give up the injections.

So Dr. Rodger convinced every colleague who had ever done a clinical trial of this procedure to combine data from all their patients, so it could be analyzed in a much more powerful way (called a patient-level meta-analysis). The result, published in The Lancet, confirms that blood thinners do not prevent pregnancy complications in high risk pregnant women, except possibly in a very small subgroup. An accompanying commentary calls the analysis “invaluable” and “compelling”.

The study is also an important example of the power of patient-level meta-analysis compared to trial level meta-analysis (which was inconclusive in this case).

“I would like to thank all of the trialists who allowed us to combine their data and all of the trial participants without which the trials would not have been done,” said Dr. Rodger, Chief and Chair of the Division of Hematology and Head of the Thrombosis Program at The Ottawa Hospital and the University of Ottawa. “This huge worldwide team has now provided definitive evidence to counsel women about blood thinner injections to prevent dreaded recurrent pregnancy complications. Generations of women can be spared the burdens and risks of daily blood thinner injections throughout pregnancy.”

Investigators: Marc A Rodger, Jean-Christophe Gris, Johanna I P de Vries, Ida Martinelli, Évelyne Rey, Ekkehard Schleussner, Saskia Middeldorp, Risto Kaaja, Nicole J Langlois, Timothy Ramsay, Ranjeeta Mallick, Shannon M Bates, Carolien N H Abheiden, Annalisa Perna, David Petroff, Paulien de Jong, Marion E van Hoorn, P Dick Bezemer, Alain D Mayhew, for the Low-Molecular-Weight Heparin for Placenta-Mediated Pregnancy Complications Study Group

Funding: Canadian Institutes of Health Research, Heart and Stroke Foundation of Canada, University of Ottawa Faculty of Medicine, The Ottawa Hospital Foundation, Pfizer, Eli Lilly Canada, Netherlands Organisation for Health Research and Development

The Ottawa Hospital: Inspired by research. Driven by compassion

The Ottawa Hospital is one of Canada’s largest learning and research hospitals with over 1,100 beds, approximately 12,000 staff and an annual budget of over $1.2 billion. Our focus on research and learning helps us develop new and innovative ways to treat patients and improve care. As a multi-campus hospital, affiliated with the University of Ottawa, we deliver specialized care to the Eastern Ontario region, but our techniques and research discoveries are adopted around the world. We engage the community at all levels to support our vision for better patient care. See for more information about research at The Ottawa Hospital.

University of Ottawa

The University of Ottawa is home to over 50,000 students, faculty and staff, who live, work and study in both French and English. Our campus is a crossroads of cultures and ideas, where bold minds come together to inspire game-changing ideas. We are one of Canada’s top 10 research universities—our professors and researchers explore new approaches to today’s challenges. One of a handful of Canadian universities ranked among the top 200 in the world, we attract exceptional thinkers and welcome diverse perspectives from across the globe.

For further information, please contact

Jennifer Ganton
Director, Communications and Public Relations
Ottawa Hospital Research Institute
Office: 613-798-5555 x 73325
Cell: 613-614-5253