Prenatal vitamins are an important source of folate and other vital nutrients during pregnancy. And many women, with the popularity of herbal medicine, take other herbs during pregnancy. Some of these herbs they may have been taking before, for an existing condition. Others, they may take to help cope with some of the physical difficulties that go with pregnancy. The following supplements and food additives should be avoided during pregnancy to avoid potential problems with the health of the baby.

• Quinine - Quinine is found in many drinks like tonic water, and these are popular as a result of their slightly bitter taste. But it was found that one woman who drunk more than 1 liter of tonic water a day whilst she was pregnant had a baby that was suffering withdrawal symptoms when it was born. It had nervous tremors within a day of being born, which disappeared two months later. Germany's BfR (Federal Institute for Risk Assessment) recommends that pregnant women treat quinine drinks, no matter how small the amount of quinine in them, as a medicinal product, and avoid them as a precaution during pregnancy.
  
• Ginseng - One of the more than 20 active constituents of ginseng was found by researchers at the Chinese University of the Hong Kong Prince of Wales Hospital to be a possible cause for concern for pregnant women. These researchers were measuring the effect of this active principle on fetal development in rats. And they found that, relating to the dose, rat embryonic development was affected. Higher doses meant a higher level of abnormalities, according to the markers of development their study used.
  Now, this study was one done on rat embryos, and so may not translate into similar effects on humans. And it only studied the effects of one of ginseng's active constituents, which was a ginsenoside called Rb1. Ginseng actually has over 20 ginsenosides, and other studies have found that these each have different actions.
  One of the difficulties with studying active constituents in herbal medicine is that the whole herbal extract may have a very different overall effect than a single constituent. This is because of the way active principles both work together and counteract each other. These two aspects, the fact that the study was not done on humans, and does not measure the overall effect of the whole ginseng extract, mean that its results should be treated cautiously. As a safety precaution, at this time it is best to at least avoid ginseng supplements during the first trimester, as the authors of the study suggest, and probably for the whole of the pregnancy. But ginseng should certainly not be branded dangerous as a result of this research as it is only a very preliminary finding in the overall picture, and more points the way as to where further research needs to be done.
  
• Ginkgo Biloba - Ginkgo biloba is another supplement that is best avoided whilst pregnant. Researchers at Wayne State University in Detroit found one of the constituents of ginkgo biloba in the placenta of women who had taken ginkgo supplements. This particular constituent, an alkaloid called colchicine, can be fatal in high doses, though medicinally, it has great anti-inflammatory effects. Other research has found that cochicine can harm a growing fetus. The potential problem with taking ginkgo supplements regularly whilst pregnant is that colchicine can build up in the womb, like caffeine when taken in excess of the recommended maximum amounts. The researchers did stress that there was no link established in the study between ginkgo and complications in the pregnancy, the study only looked at levels of colchicine in the womb.

References:
http://www.nutraingredients-usa.com/news/ng.asp?id=60554
http://www.nutraingredients-usa.com/news/ng.asp?id=25810
http://www.nutraingredients-usa.com/news/ng.asp?id=20934