Doctors Debate Use of Blood Thinners to Prevent Clots in Women After C-Sections

Nearly all women who deliver babies through cesarean section at Columbia University Irving Medical Center in New York City receive injections of the blood thinner heparin for weeks after the procedure, to prevent potentially life-threatening blood clots.

Obstetric leaders there say that’s good medical practice because the formation of those clots, called venous thromboembolism or VTE, though uncommon, is a leading cause of maternal death after delivery, particularly C-section delivery. Broad use of heparin has been shown to be effective and safe in the United Kingdom in reducing that risk and should be adopted in the U.S., they argue.

But there’s sharp debate among physicians about whether wide use of heparin is effective, worth the cost and safe, since it carries the risk of bleeding. Last year, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine recommended heparin only for women at elevated risk of VTE, citing a lack of evidence supporting near-universal use.

The controversy illustrates a classic dilemma for physicians: whether and how to adopt promising new treatments before studies have proven their safety and effectiveness. There also are questions about keeping drug company funding from influencing clinical recommendations around the drug.

The Columbia doctors were lead authors of 2016 guidelines from the National Partnership for Maternal Safety — a multidisciplinary group of medical experts — encouraging doctors to give heparin shots to all women after C-sections, except patients with specific risks. Previously, only a small percentage of mothers received them. Nearly 1.2 million U.S. women deliver via C-section each year.


Obstetricians followed other medical specialties in using heparin after surgical procedures. But the American College of Chest Physicians, whose previous guidelines had strongly advocated giving heparin to post-surgical patients, softened its support in 2012 by saying the evidence for net benefit over harm wasn’t clear.

The ACCP also acknowledged that the authors of its previous guidelines promoting heparin use had “highly problematic” financial and intellectual conflicts of interest, including financial relationships with major drug companies that produce anti-clotting drugs. To eliminate such conflicts, the ACCP sharply revised its process for choosing the experts who write its guidelines.

A controversy over drug company funding also arose in connection with the 2016 National Partnership for Maternal Safety guidelines on VTE prevention. In 2019, the editors of Obstetrics & Gynecology, which published the guidelines, disclosed that the National Partnership’s guidelines effort received funding from industry groups, including three companies that produce anticoagulant drugs — though the journal said none of the authors received any of those funds.

“We didn’t disclose the funding originally because we had no knowledge of it,” D’Alton said.

Some critics say funding from drugmakers and other health industry players casts doubt on the credibility of this and other guidelines from physician groups.

“It’s a toxic problem for medicine and the care of women,” said Dr. Adam Urato, chief of maternal and fetal medicine at MetroWest Medical Center in Framingham, Massachusetts, who pressed Obstetrics & Gynecology to disclose the partnership’s drug company funding. “Corporate cash will push guidelines toward things that are good for corporate profits, not for patients.”

Meanwhile, Canadian researchers are planning to test an alternative drug that may be equally effective, safer and cheaper in preventing VTE in women after delivery — aspirin.

Orthopedic surgeons have reported that aspirin is as effective as injectable blood thinners at preventing clots.

“I’m not against heparin, but we don’t know the best way to prevent clots,” said Dr. Leslie Skeith, an assistant professor of hematology at the University of Calgary who launched a five-nation study. “We just need better evidence.”

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