Prenatal Vitamins Explained

If you eat a healthy diet when pregnant, why do you need to take prenatal vitamins?
"Even for a woman who eats a 'perfect' diet, it is nearly impossible to get some of the nutrients in the amounts needed during pregnancy, such as iron and folic acid," Bridget Swinney, MS, RD, author of Eating Expectantly, explains in an email interview. For women who don't eat all their greens, prenatal vitamins are a kind of "insurance policy," providing them with the nutrients they may be missing from diet alone.
For example, you need more iron right now because your blood volume expands during pregnancy. Iron is an essential component of hemoglobin, the substance that carries oxygen in your blood. If your diet doesn't include enough iron-rich foods, like red meat, egg yolks, and dark leafy greens, your body will pull it from the reserves in your bone marrow. You can become anemic. Iron is especially important during the last trimester of pregnancy, when the baby's needs are the greatest, says Roy Pitkin, MD, who chaired the National Academy of Sciences' Committee on Nutritional Status During Pregnancy and Lactation.
Folic acid is absolutely critical for cell division, and for preventing neural tube birth defects such as spina bifida and anencephaly. It's best to start taking it at least one month, preferably longer, before you get pregnant and throughout your pregnancy. Health experts recommend that all women of childbearing age take daily multivitamins containing at least 400 micrograms of folic acid because pregnancies aren't always planned.  
Here are some of the vitamins and minerals and amounts you'll find in prenatal vitamins, and why your baby needs them:

Nutrient	Amount	Why You Need It
Calcium	250 mg	Builds strong bones and teeth
Choline	450 mg	Develops memory and learning center in the brain
DHA	200 mg	Promotes fetal brain development
Folic acid	600 mcg	Enables cell division and prevents neural tube birth defects
Iodine	250 mcg	Important for proper brain development
Iron	27-60 mg	Helps with the production of new blood cells to accommodate increased blood volume during pregnancy
Vitamin D	600 IU or more	Builds strong bones and teeth, and used for making hormones

Why Can't You Just Take a Multivitamin?

"A prenatal vitamin has the amount of nutrients that more closely match the nutrient needs of a pregnant woman," says Swinney. "Some may also have things that regular multivitamins don't have, like DHA [an omega-3 fatty acid] and choline, which are particularly important for fetal brain development."

Do You Need to Buy Prescription Prenatal Vitamins?

You can buy prenatal vitamins right over the counter at your local pharmacy. Or you can get a prescription from your ob-gyn, midwife, or family doctor. You'll typically pay more for prescription prenatal vitamins. Yet they do supply an extra vitamin and mineral boost. "Prescription prenatals tend to have more vitamins and minerals included, or more of certain nutrients than an over-the-counter brand," Swinney says. You may find more folic acid (1,000 micrograms instead of the 400 micrograms in over-the-counter versions) and iron in prescription prenatal vitamins and supplements, as well as added nutrients like iodine, choline, magnesium, and copper. 

How Safe Are Prenatal Vitamins?

Generally, prenatal vitamins are very safe. Many of the vitamins in them, including vitamin C and the B vitamins, are water soluble, which means your body will flush out any extra you consume. Where you do need to watch that the vitamin doesn't exceed the recommended daily allowance for pregnant women is with the fat-soluble vitamins: A, D, E, and K. Because your body does store these vitamins, it is possible to get more than you need.
Too much of a good thing is never a smart idea. Don't pop handfuls of vitamins and supplements and then eat nutritional bars, because you could overdose on certain nutrients. Let your doctor know about all of the vitamins and supplements you're taking so that he or she can help you keep track of them.
Prenatal vitamins can cause some minor side effects like constipation and nausea, which can already be issues during pregnancy. "If your nausea is worse in the morning when you get up, don't take it when you get up. Take it before bed or with food," Pitkin advises. You can also try a liquid or chewable prenatal vitamin if it's easier for you to take. If constipation is a problem, add fiber to your diet by eating more fruits, vegetables, and whole grains.

Why Prenatal Vitamins Aren't Enough

Just because you're popping a prenatal vitamin every morning, don't think your diet is off the hook. Prenatal vitamins are no substitute for three healthy meals. They don't contain the protein, calories, or all of the nutrients you and your baby need during this time.
"Even the best prenatal vitamins don't have every single nutrient found in food," Swinney says. "There are hundreds of antioxidants found in food that aren't in vitamins. Also, prenatal vitamins don't contain much calcium, so calcium-rich foods like milk and yogurt are a must." Eat a variety of fruits, vegetables, whole-grains, dairy, and protein to ensure you're getting everything you and your baby need, and then you can think of your prenatal supplement as an added nutrient bonus.