If there's one thing women can count on during pregnancy, it's that someone somewhere will tell them to take prenatal vitamins. It could be their doctor, their mother or a well-meaning stranger; this advice is something we've all heard and may have even said ourselves.

But do you know what's included in prenatal vitamins?

Moms-to-be tend to be very concerned about what they put into their bodies, so it's only natural to be curious about these nutrients. Here's what's likely included in your vitamins and how to find the type you need:

The prenatal vitamins you absolutely need

These vitamins are especially important for your health during pregnancy and your baby's development. Here's what you need and how much, as recommended by the American College of Obstetricians and Gynecologists.

Iron: 27 milligrams daily

It's hard to get enough of this nutrient in your natural diet, which is why it's in most - if not all - prenatal vitamins. Iron helps deliver oxygen throughout the body, which you and your baby need a lot of. If you don't get enough, you could suffer from iron-deficiency anemia, which increases your risk of low birth weight, preterm delivery and infant mortality.

Calcium: 1,00 milligrams daily

Calcium supports bone, nerve and muscle growth for mom and baby, so you'll need a little extra while you're pregnant. Otherwise, you may lose bone density as all the calcium in your body reroutes to the developing baby.

Folic Acid: 60 micrograms daily

This vitamin is important for proper neural tube development. A defect seriously affects the baby's brain and spinal cord.

In fact, it's good for women who may be or are actively trying to become pregnant to make sure they get a good amount of folic acid, whether from vitamins or foods like leafy vegetables, citrus fruits, beans and nuts. This is because neural tube defects develop before many women knowing they're pregnant, so supplementing after a pregnancy test may be too late. 

Vitamin D: 600 international units daily

Like calcium, this fat-soluble vitamin builds your baby's bones and teeth. Not consuming enough vitamin D during pregnancy puts your baby at risk of a deficiency at birth. This can delay her physical development, cause abnormal bone growth or lead to rickets. 

A vitamin D deficiency may also increase your risk gestational diabetes and preeclampsia. More research is needed to prove this link, but it's better to be safe than sorry, after all!

Other vitamins that can help during pregnancy

Unfortunately, not all vitamins are created with the same ingredients. Prescription ones are regulated by the Food and Drug Administration, meaning they're required to contain certain nutrients. However, over-the-counter brands may have some additional vitamins that support a healthy pregnancy and your baby's development.

Copper

You won't need much additional copper (What to Expect recommends 2 milligrams a day), but given that this mineral helps form blood cells, you might want to look for it in your supplements.

Fatty acids

Most prenatal vitamins don't contain omega-3 fatty acids, so you may need to use a separate supplement or add more to your diet. Natural sources of omega-3s include nuts, beans and seeds. Fish has a lot of omega-3s as well, but be careful not to consume too much as they also contain mercury.

Iodine

Given that about one-third of pregnant women in the U.S. are iodine deficient, the American Association of Pediatrics recommends pregnant and breastfeeding women add this vital nutrient to their diet and supplements to get at least 150 micrograms daily. Iodine helps your baby's brain and thyroid development. 

Vitamin A

Another fat-soluble nutrient, vitamin A helps your baby develop its heart, eyes, lungs, bones, kidneys and respiratory, circulatory and central nervous systems. It also helps you repair tissues after giving birth. You probably don't need to supplement much as you can easily get enough vitamin A from a healthy diet. In addition, too much has been linked to birth defects. Talk to your doctor if you think you need to supplement this nutrient. The safest form of vitamin A is beta carotene. 

Vitamin C

This is one of the easiest vitamins to get in your diet, and in fact, taking too much can be dangerous for your baby. According to What to Expect, a pregnant woman requires 85 milligrams of vitamin C per day, so keep this in mind when looking at your prenatal vitamin options.

Zinc

Zinc contributes to your baby's cell growth and DNA production. As your child grows from a fertilized egg to a full human infant in approximately nine months, it's no wonder many medical specialists recommend adding this mineral to your diet. 

Finding the right prenatal nutrients

You can get prenatal vitamins via a doctor's prescription or over the counter. Prescription vitamins will likely contain the four essentials (iron, calcium, folic acid and vitamin D), and possibly some of the others. 

So how do you know which ones to take? The answer, of course, is to talk to your doctor. He or she may recommend a mix of prescription and specific over-the-counter supplements to make sure you're getting the proper nutritional requirements for pregnancy.