During pregnancy, the vitamin that should be avoided is too much amounts is supplemental Vitamin A.
During pregnancy, the only vitamin that should be avoided is too much amounts is supplemental Vitamin A. There are foods that include Vitamin A as part of the enrichment process and thus the food labels need to be read before eating enriched foods.
Vitamin A in large doses as a supplement has been shown to have a potentially negative effect on fetal development. Carrots and vegetables, on the other hand, do not contain vitamin A itself but carotene. Carotene is provitamin A and is converted to vitamin A in your body only if your body needs it. You cannot get too much Vitamine A by eating Carotene because the body regulates conversion from carotene to Vitamin A. Although carotene is converted to vitamin A in the body, excessive ingestion of carotene causes carotenemia, not vitamin A toxicity.
Liver and other meats do contain vitamin A, so by eating those you could ingest a larger amount of vitamin A. Eating carrots and vegetables cannot do any harm to your baby.
Other vitamins that could cause a problem due to build up in the body are Vitamins D, E and K.
When supplemental Vitamin A is added to the prenatal vitamin, overdose can occur in as little as 4 times the regular dose. If Vitamin A is consumed in amounts greater than 10,000 IUs, liver toxicity or fetal birth defects can occur. Vitamin A is consumed in common foods like meat, fish and eggs. Fortified cereals also add Vitamin A. This means it is relatively easy to reach that upper level without trying to.
Vitamin D and toxicity is a heavily studied topic. The upper level of Vitamin D supplementation is set at 2,000 IUs a day. The human body can produce 20,000 IUs of Vitamin D if exposed to the sun without clothing in one shot. Herein lies the trouble with supplementation. Vitamin D toxicity does occur, but due to the overwhelming conflict in studies, Vitamin D supplementation is not recommended in pregnant women.
Vitamin E supplementation is just as tricky as Vitamin D supplementation. There are two forms of Vitamin E supplements, synthetic and natural. Natural vitamin E is more readily absorbed by the body, but most supplements contain the synthetic version. There is a link between babies with heart defects and supplemental Vitamin E. In a recent study, women who took supplemental Vitamin E (over and above their prenatal vitamin) were 70% more likely to give birth to a baby with a heart defect.
Too much Vitamin K is associated with babies having worse cases of jaundice. Jaundice is a yellowing of the skin due to a buildup of bilirubin in the body.