More is not better when it comes to vitamins. Many patients come in with bottles of different vitamins - some take 20 different vitamins a day.
One multivitamin with at least 400 micrograms of folic acid and no more than 5000 IU of vitamin A (vitamin A is a teratogen - it can cause birth defects if consumed in high amounts - most multi and prenatal vitamins have less than or equal to 5000 IU of vitamin A daily, most in the form of beta carotene, the safest form of vitamin A) is all that is needed and desired.
Some ask if they must be on a prenatal vitamin, or is a multivitamin enough. I recommend a preconceptual multi and not a prenatal until you get pregnant, because some patients get nausea or constipation from prenatals and then become noncompliant with vitamins all together.
400 micrograms of folic acid is all you need preconceptually, and once you get pregnant, all prenatal vitamins have a full milligram (1000 micrograms) of folic acid. Women who have a family history of neural tube defects (spina bifida, anencephaly) should take 4 milligrams (4000 micrograms) of folic acid daily, as should women with epilepsy on anti-seizure medications. Remember that 1mg or above of folic acid is not over the counter and you will need a prescription from your doctor.
In women who can't tolerate vitamins, we can write a prescription for folic acid alone, which is well tolerated.