What's the difference between over-the-counter prenatal vitamins and prescription prenatal vitamins? Is the difference important?
The studies that have indicated a benefit of folic acid (folate) decreasing the chance of miscarriage and organ abnormalities (specifically, neurotube defects such as spina bifida) have shown that the minimum dosage to acquire this added protection is 400 micrograms (4/10 of a full milligram) a day. Regarding folic acid, over-the-counter vitamins have this 400 micrograms dose, but prescription vitamins have a full 1000 micrograms (1 milligram). So the advantage to the prescription vitamins is more than enough folate. These also have more iron, as well as formula mixes of other vitamins that have been tested extensively by large corporations who have spent a whole lot of money to ensure a good, safe product. Because the dosages are larger, and therefore prescription, they also have to deal with extra FDA scrutiny, which of course is to your and your baby's benefit.
The problem with prescription vitamins is that some women have trouble tolerating them (nausea, constipation, etc.), so sometimes it's better for a woman's nutrition to use the non-prescription vitamins until the side effects subside to the point where she can try a DIFFERENT brand-name prescription vitamin. (Remember, it's better to get your nutrition from food than only from vitamins when you're nauseated.) Because not all brand-name prescription vitamins will be tolerated the same, there should be one with your name on it. Don't give up on them all because you can't tolerate a particular one.
If you must, choose an over-the-counter multivitamin with the 400 micrograms of folate and some iron. Once again, use a big company brand. Stay away from the health food concoctions recommended by self-appointed experts behind the counters of their own shops. They're neither doctors, nutritionists, nor obstetricians, unless they have diplomas stating so.
(For example, too much Vitamin A can affect the growth of the baby. Too much iron can deposit iron in other organs of a woman's body. These are the things that the big companies have worked out with billions of dollars worth of research.)
If you can't tolerate ANY vitamins, remember that we got by for millions of years worth of pregnancies without them. But let's not go back to those days, vitamins-wise, unless there's no other choice. The point is that vitamins are not a deal-breaker, but they're a terrific idea.