You need the same vitamins and minerals during pregnancy as you do when you aren't pregnant, but in some cases you need more or less of these nutrients. Getting too much of certain vitamins may be risky during pregnancy, but understanding which nutrients are of concern and avoiding high-dose supplements of these vitamins can help you avoid any adverse effects.
You need vitamin A for the healthy growth and development of your baby's organs, bones, eyes, nervous system, circulatory system and respiratory system. You don't need more than 10,000 international units per day: Getting too much retinol, or preformed vitamin A, can cause birth defects. Your prenatal vitamin will contain at least some vitamin A, so don't take any other supplements containing this vitamin. Don't worry about the vitamin A you get from the beta-carotene and other carotenoids in fruits and vegetables. Your body only turns carotenoids into vitamin A if you need it, so beta-carotene won't cause toxicity symptoms.
Vitamin E may help some women avoid pregnancy complications, such as preeclampsia, when taken late in pregnancy. An article published in the "European Journal of Obstetrics, Gynecology, and Reproductive Biology" in October 2012 recommends against this practice as it could cause other adverse effects. MedlinePlus recommends that you not take supplemental vitamin E earlier in pregnancy, stating that it may harm your baby, although the evidence is preliminary. A study published in "Reproductive Toxicology" in 2005 found that vitamin E supplementation doesn't appear to cause birth defects but that at high doses it may be associated with having a low-birth-weight baby.
You need to get the recommended amount of vitamin B-6 for your baby's brain and nervous system to develop properly, which is why most prenatal vitamins contain at least 100 percent of the daily value of 1.9 milligrams. Some women also try taking this vitamin to help relieve vomiting and nausea. Getting too much of this vitamin may cause nerve damage and numbness. Talk to your doctor before taking more vitamin B-6 than is in your prenatal vitamin, and don't take more than the tolerable upper intake level of 100 milligrams per day.
Other Vitamin Considerations
Not getting the correct amount of essential vitamins and minerals may be just as risky as getting too much of these nutrients. Take a prenatal vitamin -- and eat a balanced diet -- but don't take any other supplements unless recommended by your doctor, so you get the nutrients you need without overdosing on any one nutrient.