Prenatal vitamins typically contain a core set of nutrients: folic acid, iron, calcium, vitamin D, iodine, choline, omega-3 fatty acids (particularly DHA), several B vitamins, vitamin C, zinc, and magnesium. The exact amounts vary by brand, but each ingredient targets a specific need during pregnancy, from building your baby’s brain and spine to supporting the increased blood volume your body produces. Here’s what each one does and how much you need.
Folic Acid
Folic acid is the single most important nutrient in a prenatal vitamin. It helps the neural tube, the structure that becomes your baby’s brain and spine, develop correctly during the first few weeks of pregnancy. Neural tube defects like spina bifida happen so early that they can occur before you even know you’re pregnant, which is why the CDC recommends all women capable of becoming pregnant get 400 micrograms (mcg) of folic acid every day.
If you’ve had a previous pregnancy affected by a neural tube defect, the recommendation jumps to 4,000 mcg daily, starting at least three months before conception. Folic acid is the synthetic form of folate, and it’s the only form that has been shown to prevent these birth defects. You’ll find folate in leafy greens and fortified grains, but a supplement ensures you hit the target consistently.
Iron
Your blood volume increases by roughly 50% during pregnancy, and iron is essential for making the extra red blood cells that carry oxygen to your baby. The recommended daily amount for pregnant women is 27 milligrams, up from 18 mg for non-pregnant women of the same age. Most prenatal vitamins contain this full amount or close to it.
Iron is also one of the nutrients most likely to cause side effects like constipation or nausea. Taking your prenatal with food or before bed can help. If you’re diagnosed with iron-deficiency anemia during pregnancy, your provider may recommend additional iron on top of your prenatal.
Calcium and Vitamin D
Calcium builds your baby’s bones and teeth, and if you’re not getting enough from food, your body will pull it from your own bones to meet fetal demand. The target is 1,000 mg per day for women ages 19 to 50 (1,300 mg for those 14 to 18). Most prenatal vitamins contain only a fraction of this because calcium is a bulky mineral that would make the pill enormous. You’ll likely need to make up the difference through dairy, fortified plant milks, or a separate supplement.
Vitamin D helps your body absorb that calcium and plays a role in immune function. Most prenatal vitamins include about 400 IU per tablet, which is a baseline amount. Some newer formulations contain more, but there isn’t strong enough evidence yet to recommend high-dose vitamin D supplementation across the board during pregnancy.
Choline and Iodine
These two nutrients have gotten more attention in recent years, and for good reason: both are critical for fetal brain development, and many prenatal supplements fall short. A University of Colorado analysis found that fewer than half of prenatal supplements on the market contain adequate amounts of either one.
The recommended intake for choline during pregnancy is 450 mg per day. Choline supports brain development and helps prevent certain birth defects. Eggs, liver, and soybeans are good dietary sources, but most people don’t eat enough to hit 450 mg without a supplement. For iodine, the target is 220 mcg per day during pregnancy, up from 150 mcg for non-pregnant adults. Iodine is essential for your baby’s thyroid function and brain growth. If your prenatal doesn’t list choline and iodine on the label, it’s worth checking or choosing one that does.
DHA (Omega-3 Fatty Acid)
DHA is a type of omega-3 fat that plays a major role in building your baby’s brain and eyes, especially during the third trimester when brain growth accelerates. Several organizations, including the March of Dimes and the American Academy of Pediatrics, recommend pregnant women get at least 200 to 300 mg of DHA per day.
Not all prenatal vitamins include DHA. Some brands sell it as a separate softgel alongside the main prenatal pill. If your prenatal doesn’t contain DHA, eating two to three servings of low-mercury fish per week (like salmon, sardines, or herring) is the most reliable dietary source.
B Vitamins
Beyond folic acid (which is technically vitamin B9), prenatal vitamins usually contain vitamin B6 and vitamin B12. Vitamin B6 is involved in nervous system development and the production of brain-signaling chemicals. It’s also commonly used as a first-line approach for managing nausea and vomiting during pregnancy. The evidence that it reliably eliminates morning sickness is mixed, but it does appear to provide some relief for many women.
Vitamin B12 supports red blood cell formation and neurological development. It’s especially important if you follow a vegetarian or vegan diet, since B12 is found almost exclusively in animal products.
Vitamin A
Vitamin A supports your baby’s eye development, skin growth, and immune function, but it comes with an important caveat: too much of the preformed type (retinol) during pregnancy has been linked to birth defects. Most well-designed prenatal vitamins use beta-carotene instead, which your body converts to vitamin A only as needed, eliminating the toxicity risk. If you’re taking any additional supplements, check that your total retinol intake isn’t excessive.
Vitamin C, Zinc, and Magnesium
Vitamin C supports your immune system and helps your body absorb iron from plant-based foods, which makes it a useful companion to the iron in your prenatal. Zinc contributes to cell growth and immune function, both of which are in high demand during pregnancy. Magnesium supports hundreds of enzyme reactions in the body, including those involved in muscle and nerve function. Most prenatal formulas include moderate amounts of all three, though like calcium, magnesium can be difficult to fit into a single pill at full recommended levels.
When To Start Taking Them
Ideally, you should start a prenatal vitamin before you conceive. The Mayo Clinic recommends beginning folic acid supplementation at least three months before pregnancy, since the neural tube forms in the earliest weeks, often before a missed period. If you’re not actively planning a pregnancy but could become pregnant, taking a daily supplement with at least 400 mcg of folic acid covers the most critical window.
Throughout pregnancy, a prenatal vitamin acts as nutritional insurance. It doesn’t replace a balanced diet, but it fills the gaps that are nearly impossible to close through food alone, particularly for iron, folic acid, choline, and iodine. When choosing a prenatal, look at the label for those four nutrients specifically, since they’re the ones most likely to be missing or underdosed.