If you're pregnant and taking the herb known as ginkgo Biloba, caution is urged. Alternative Healing Today warns:

Ginkgo biloba pregnancy has been the subject of many controversial studies including the move to determine the effects of ginkgo biloba pregnancy. But for safety measures, pregnant and lactating women are generally advised to refrain from taking ginkgo biloba pregnancy extracts. Safety dosage for use in pregnancy has not been established in ginkgo biloba pregnancy supplements.

The Ginko Biloba pages offer this rather scientific paragraph about the medicinal use of the herb:

Ginkgo leaf extracts have been shown to have a wide range of biological activities. The most well-known use is the ability to improve short term memory. Other important effects include a protective effect on the blood-brain barrier and an anti-radical (antioxidant) effect.