Researchers have found high doses of a particularly harmful compound in the placental blood of women taking the herbal remedy Ginkgo biloba.

Previous research has shown that the compound, called colchicine, can harm a developing fetus.

While the new study provides no direct evidence that ginkgo taken during pregnancy causes birth defects, the scientists say expectant mothers should consider avoiding the supplement.

"If you're pregnant or planning on getting pregnant, you probably should think about this before you take ginkgo," said Howard Petty, a professor of biological sciences at Wayne State University in Detroit. Petty is a co-author of the study appearing in the September issue of the journal Chemical Research in Toxicology, published by the American Chemical Society.

"During pregnancy, both the woman and the fetus are vulnerable, so extra caution should be observed," he said.

Colchicine, an alkaloid, is one of several powerful anti-oxidant and anti-inflammatory agents found in ginkgo. At higher doses it can prevent cell growth and in even higher doses can be fatal, the researchers said. The substance is not normally found in humans but is present in nearly 200 species of plants.

Herbalists going back to Chinese practitioners 4,800 years ago have touted ginkgo as a memory enhancer that increases blood flow to the brain. More recently, several trials have suggested the herb might help prevent or limit the extent of dementia in elderly patients. The herb also acts as a blood thinner, however, which has caused problems for some patients who also take other blood-thinning prescriptions.

Petty and co-author Shahriar Mobashery, director of the Institute for Drug Design and a chemistry professor at Wayne State, suggest that the situation for pregnant women may be similar to drinking coffee. While caffeine is rapidly cleared from the mother's system, it can build up in the womb.

"The thing is, if you know colchicine is there, you're not going to take it," Petty said. "But if you don't know it's in these herbal medicines, suddenly you're exposed to it and you could have some problems. It's not that taking herbal medicines are bad, it's just that you have to know what you're taking."

For their study, the researchers took placental blood samples from 24 new mothers in the Detroit area. Measurements found that the five women who regularly took ginkgo supplements had colchicine levels ranging from 49 to 763 micrograms per liter of placental blood. Among the remaining 19 women, including several who were vegetarians, the levels averaged less than 2 micrograms of colchicine.

The researchers also analyzed one brand of ginkgo extract tablets that some of the women were taking and found each contained approximately 26 micrograms of the compound.

Herbal supplements are considered food rather than drugs under U.S. Food and Drug Administration regulations, and there's no official standard for doses or ingredients of the supplements. Other research has shown that the strength of herbal remedies can vary widely from brand to brand, or even from batch to batch of the same brand, although some manufacturers have been trying to produce more standardized doses.

　　From Wyne.edu