There are no formal rules for what makes an ordinary multivitamin different from a prenatal supplement. In general, most prenatal supplements contain more folic acid, iron, and calcium than you'll find in a standard adult multivitamin. Pregnant women need more of these nutrients than usual -- specifically more than twice as much folic acid -- also called folate -- and 50 percent more iron to make more blood to nourish the fetus. Calcium needs stay steady at 1000 milligrams to prevent bone loss late in pregnancy.

When it comes to pregnancy, timing is everything. For example, neural tube defects such as spina bifida can develop in an embryo before a woman even knows she's pregnant. That's why doctors encourage women to start taking prenatal supplements, or at least folate -- also known as folic acid -- for at least a few months before getting pregnant. Taking folic acid, a B vitamin, both before and during pregnancy, greatly reduces the chance that your baby will be born with spinal bifida or other neural tube defects.

Every woman of childbearing age should have 400 micrograms of folic acid a day, and if you're trying to get pregnant, take at least that much. Most prenatal vitamins contain 800 mcg. The U. S. Food and Drug Administration recommends taking no more than 1 mg (1,000 mcg) per day.

According to a report by the Institute of Medicine, the organization that recommends federal guidelines for nutrition, most pregnant women should be able to get enough nutrients through food alone -- with the exception of iron. (In their last two trimesters, pregnant women need to absorb about 3 mg more iron every day than most people get from food alone.) However, the truth is that few Americans eat the kinds of foods that would supply all these nutrients. That's why most healthcare providers recommend that pregnant women take a prenatal supplement. With today's busy lifestyles, it can be difficult to get enough vitamins and minerals from just your diet, and a supplement is an easy form of "insurance."

Before you start taking any supplement, consult your doctor to ensure it won't do more harm than good and won't interact with other medications you may be taking. If you're expecting twins, for example, you may need a special type with different amounts of certain nutrients. Doctors will also typically check to see whether iron deficiency is a problem through blood tests in your initial visit and again when you are about two thirds of the way through pregnancy. These blood tests can help you know whether or not you need to take iron supplements as your pregnancy continues into the third trimester.

If your doctor writes you a prescription, your supplements may be covered by your insurance.(Of course, a wide variety of prenatal supplements are available at drugstores without a prescription). Once you and your doctor decide which supplement is best for you, read the directions before you start taking them; some brands require you to take up to six pills per day.

Keep in mind that taking a supplement isn't a guarantee you'll be getting everything you need. In fact, most prenatal supplements only have 15 to 25 percent of the daily value of calcium, and you still need to make up the difference with food rich in the mineral, such as milk, yogurt, broccoli, lentils, and spinach -- or by taking additional calcium.

The bottom-line is that supplements aren't an efficient way to get major nutrients, and you shouldn't rely on them to replace balanced meals. Try to eat five fruits and vegetables a day and eat as many whole grain foods as possible.

Prenatal supplements vary widely from brand to brand. Besides iron, calcium, and folic acid, they often contain:

•Vitamins A, C, D, and E (Prenatal vitamins generally contain 3,000 to 5,000 IU, which women can supplement with foods high in vitamin A. More than 8,000 IU of preformed vitamin A (retinol and retinyl esters) can be harmful to a developing fetus, so be sure to check the label. The FDA recommends that pregnant women get their vitamin A in the form of beta-carotene, which is found in fruits and vegetables and is not considered toxic.

•Other B vitamins including thiamine (B1), riboflavin (B2), pantothenic acid (B5), B6, and niacin (B12)

•Important minerals including copper, magnesium, selenium, and zinc.

Certain forms of iron (including ferrous fumarate and ferrous gluconate) are less likely to cause upset stomach and nausea than the form most commonly used, ferrous sulfate. Slow release iron pills cost a little more, and some women can tolerate them better than the regular kind.

You may also prefer to pay more for pills containing calcium citrate malate because it's easier to absorb than calcium carbonate and doesn't need to be taken with meals. (This is best if your supplement has iron too). In addition, it's far less likely to have toxic heavy metals such as lead, cadmium, or mercury than brands containing unrefined calcium from oyster shells, bone meal, or the mineral dolomite.

Some prenatal supplements sold at natural food stores even contain herbs such as ginger and red raspberry, plant products such as wheat grass, and beneficial bacteria such as lactobacillus. If you're thinking of taking complex supplements like these, please consult with your doctor first.

Follow the directions on your particular bottle, but bear in mind that because all those nutrients are jostling each other in your stomach, you probably won't get everything the label promises.

If you're relying on your supplement for extra iron, you'll probably want to take it between meals so more will get absorbed. Taking extra iron may cause constipation, so drink a lot of water throughout the day. Another thing to consider is that caffeine hinders iron and calcium absorption, so avoid having tea and coffee before or after you take your pill. Taking your pills with milk isn't a great idea either because it interferes with iron and zinc absorption. Juice or water are best.

If you're having trouble keeping your pill down, try a different type. You can also try taking it at different times of the day, like in the afternoon or evening if you're too queasy in the morning. There are even chewable tablets or liquid forms available if you can't swallow large pills. If these steps don't help, consider taking smaller supplements tailored to your needs. Getting enough folic acid is most critical during the first trimester (to prevent birth defects), and iron is most important in the last two (to form additional blood). Calcium is important all through pregnancy -- your bones store extra amounts early in pregnancy and divert it to your baby in the last trimester, when the skeleton develops. Ask your doctor for advice on how to get enough.

If you simply can't tolerate supplements, there's always the old-fashioned route. Getting your nutrition from food is the tastiest way to do it, and the vitamins and minerals are in the form that is easiest for your body to absorb. Eating a good diet may not be as hard as you think. Now that the FDA has required grain products to be fortified with folic acid, it should be easier for women to get enough from cereals, bread, and pasta; consult your doctor about your meal plan or take a folic acid supplement by itself. Cooking food in cast iron will increase the amount of iron in your food considerably, and eating iron-rich foods with vitamin C will help you absorb more. Three to four servings of dairy each day should get you all the calcium you need during your pregnancy, and five to nine servings of fruits and vegetables should provide those vitamins and minerals. If you're a vegetarian, it's a good idea for you to consult a nutritionist for some personal advice.

-- Deepi Brar is multimedia editor at Consumer Health Interactive.

References

First published December 19, 2002
Last updated November 30, 2007
Copyright © 2002 Consumer Health Interactive

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