Study: Blood Thinners Don’t Prevent Miscarriage

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April 28, 2010 — For women with a history of miscarriages, taking aspirin alone or combined with the blood-thinning drugheparin fails to prevent pregnancy loss, new researchshows.

The findings were published in the April 29 issue of the New EnglandJournal of Medicine.

Five percent of women have had two recurrent miscarriages, and 1% have hadthree recurrent miscarriages, but the causes are unknown.

Aspirin and heparin have been prescribed to women with unexplained recurrentmiscarriages in the belief that the miscarriages were related to blood clotsdeveloping in the uterine blood vessels.

Aspirin and heparin both thin the blood, reducing the risk of clots.However, there is little evidence on whether this treatment reducesmiscarriage.

Blood Thinners and Miscarriage

To test this theory, researchers led by Stef P. Kaandorp, MD, of theUniversity of Amsterdam in the Netherlands, compared 364 women ages 18 to 42who had histories of unexplained recurrent miscarriages. The women also had nodiagnosed uterine disease or antiphospholipid syndrome, animmune system disorder that increases a woman’s risk for blood clots andpregnancy loss.

The women were randomly assigned to one of three treatments: low-doseaspirin with heparin, low-dose aspirin only, or a placebo. Those who receivedthe combination treatment reported more side effects, including bruising,swelling, or itching where the heparin wasinjected.

The women considered eligible for the study had either not yet conceived orwere less than six weeks into their pregnancies. Eventually, 299 women werepregnant during the course of the study; nearly two-thirds of this groupsuccessfully gave birth to a live infant. The study took placebetween 2004 and 2008 at eight hospitals in the Netherlands.

However, live birth rates did not differ between the three treatment groups,suggesting heparin and/or aspirin do not offer any significant benefit:

  • 54.5% of the aspirin-heparin group successfully gave birth.
  • 50.8% of the aspirin-only group successfully gave birth.
  • 57% of the placebo group successfully gave birth.


Better Prevention Needed

In an accompanying editorial, I.A. Greer, MD, of Hull York Medical School inthe U.K., said the findings leave doctors and researchers going back to thedrawing board.

“The widespread use of antithrombotic interventions for women with two ormiscarriages,” Greer writes, “appears to be no more than another false start inthe race to identify an effective intervention for this distressing conditionthat affects so many women.”

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