Study: Blood Thinners Don't Prevent Miscarriage
Though Often Prescribed to Women With Previous Miscarriages, Aspirin and Heparin Don't Prevent Them
April 28, 2010 -- For women with a history of miscarriages, taking aspirin alone or combined with the blood-thinning drug
heparin fails to prevent pregnancy loss, new research
The findings were published in the April 29 issue of the New England
Journal of Medicine.
Five percent of women have had two recurrent miscarriages, and 1% have had
three recurrent miscarriages, but the causes are unknown.
Aspirin and heparin have been prescribed to women with unexplained recurrent
miscarriages in the belief that the miscarriages were related to blood clots
developing 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 reduces
Blood Thinners and Miscarriage
To test this theory, researchers led by Stef P. Kaandorp, MD, of the
University of Amsterdam in the Netherlands, compared 364 women ages 18 to 42
who had histories of unexplained recurrent miscarriages. The women also had no
diagnosed uterine disease or antiphospholipid syndrome, an
immune system disorder that increases a woman’s risk for blood clots and
The women were randomly assigned to one of three treatments: low-dose
aspirin with heparin, low-dose aspirin only, or a placebo. Those who received
the combination treatment reported more side effects, including bruising,
swelling, or itching where the heparin was
The women considered eligible for the study had either not yet conceived or
were less than six weeks into their pregnancies. Eventually, 299 women were
pregnant during the course of the study; nearly two-thirds of this group
successfully gave birth to a live infant. The study took place
between 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 in
the U.K., said the findings leave doctors and researchers going back to the
“The widespread use of antithrombotic interventions for women with two or
miscarriages,” Greer writes, “appears to be no more than another false start in
the race to identify an effective intervention for this distressing condition
that affects so many women.”