What Is the Difference Between Over-the-Counter Prenatal Vitamins & Prescription Prenatal Vitamins?

Pregnant women can have difficulties getting enough of two essential nutrients -- iron and folic acid -- through food alone. You need iron to make red blood cells, and folic acid helps prevent birth defects. Pregnant women have approximately 50 percent more blood than non-pregnant women, which increases their iron needs from 18 milligrams per day to 27 milligrams per day. Taking a prenatal vitamin can ensure you get enough of these and other essential micronutrients. Understanding the differences between over-the-counter and prescription prenatal vitamins can help you decide which is best for you.

Micronutrient Content

Prescription prenatal vitamins often contain up to 1,000 micrograms of folic acid, which is the most you should take per day, but OTC versions usually contain no more than 800 micrograms. This is still more than the minimum recommended of 600 micrograms per day. These vitamins may also have a higher iron content, with 30 milligrams or more. The higher iron can make you constipated or upset your stomach, so find a version with less iron if you're not anemic and experience stomach problems. Don't take supplements that contain more than the tolerable upper intake level of 45 milligrams unless your doctor tells you to, as doing so could increase your risk for preeclampsia, miscarriage and gestational diabetes.

Ingredients to Limit

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Choose a prenatal vitamin that doesn't contain more than the tolerable upper intake level of 10,000 international units per day of preformed vitamin A, or retinol, which can cause birth defects affecting the lungs, eyes, heart or skull. Vitamin A in the form of beta-carotene isn't likely to cause adverse effects. OTC versions of prenatal vitamins, especially those sold in health or natural food stores, may contain additional herbs, which isn't recommended because they haven't been tested thoroughly for safety, according to eMedTV. Herbs to be cautious of include stinging nettles, chamomile and dandelion, even though they are sometimes recommended to pregnant women by midwives and herbalists.

Truth in Labeling

Because of its higher micronutrient content, prescription vitamins are more closely regulated by the U.S. Food and Drug Administration, so they may be more likely to contain the ingredients in the amounts listed on the label. A study conducted at Boston University in 2009 found that many prenatal vitamins, including some prescription versions, didn't contain the amount of iodine listed on the label, and those that contained kelp as a source of iodine were more likely to have less than the amount listed than those listing potassium iodide. Pregnant women who don't get the recommended 220 to 290 micrograms of iodine per day may be more likely to have children who suffer from mental retardation and growth problems.

Cost Considerations

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OTC prenatal vitamins cost less than prescription prenatal vitamins, making them a more affordable choice for women without insurance or with limited insurance coverage. Some insurance companies cover most or all of the cost of prescription versions of prenatal vitamins, however, so ask your doctor to recommend a few prenatal vitamin choices and check your insurance coverage to see which vitamin is the least expensive.