updated 3/8/2004 4:41:28 PM ET 2004-03-08T21:41:28

Women with genetic flaws that make them prone to blood clots are at increased risk of multiple miscarriages, a study suggests.

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The researchers recommended that women who have at least two miscarriages be tested for the two flaws, either of which doubles the risk of repeat pregnancy loss.

About 5 percent of U.S. women of childbearing age have two or more miscarriages, and no cause can be found in more than half the cases. It is unclear how many unexplained cases are due to clotting mutations, but the portion is likely significant, said Dr. George Kovalevsky, an assistant professor of obstetrics and gynecology at Eastern Virginia Medical School.

Most carriers of the flaws have no symptoms and would not be tested unless they had a family history of blood clots. Testing is simple but costly, roughly $200 for each mutation.

Evidence suggests that blood-thinning medicine including aspirin and more potent drugs might improve the chances for a healthy pregnancy, the researchers said, though that was not examined in their research.

The study was an analysis of 23 previous papers involving more than 2,500 women with recurrent miscarriages and one of two gene mutations. It appears in Monday’s issue of Archives of Internal Medicine.

Not all previous studies found that carriers were prone to multiple miscarriages, but pooling the results showed the association was strong, the researchers said.

Testing recommended
Roughly 8 percent of white Americans, or about 18 million people, are carriers of one of the two mutations — Factor V Leiden and prothrombin, the two most common causes of inherited thrombophilia, a tendency to develop blood clots.

Minorities are much less likely to be carriers, said Kovalevsky, who led the research while he was at the University of Pennsylvania.

Carriers have one copy of the mutation. People with the full mutation, or two copies, are much more rare and more likely to develop symptoms, he said.

“Given the clinical implications and the relatively high prevalence of these mutations, we recommend testing women with recurrent pregnancy loss for their presence,” the researchers said.

Petra Smeltzer, a 42-year-old Washington-area woman with no history of blood clots, had five unexplained miscarriages starting about seven years ago that devastated her and puzzled her doctors. Fertility tests turned up nothing abnormal.

“They just couldn’t figure it out,” said Smeltzer, who remains childless. “They said it was my age and that I needed to do in-vitro fertilization.”

Blood tests ultimately showed she carries three mutations including prothrombin and Factor V Leiden, plus an autoimmune disorder that she thinks contributed to the problem.

Dr. Sandra Carson of Baylor College of Medicine said treating mothers-to-be with blood thinners is controversial because there is no definitive proof that it improves their chances of having children.

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