Learn about the benefits of taking prenatal vitamins when you're trying to conceive. Explore the known side effects and discover how prenatals can affect your body.


Dr. Naz Homaifar

We’re not talking Flintstones for Kids. We’re talking about supplements. More specifically, the prenatal vitamins that the Centers for Disease Control (CDC) and the American College of Obstetrics and Gynecology (ACOG) recommend starting at least one month before trying to get pregnant. We’re  going to walk you through what to look for in a prenatal vitamin, the side effects you might experience, what to do about them, and how not to pay way more than you need to.

Why take prenatal vitamins?

Pregnancy is a big ask for your body—you have to nourish not only yourself, but also your growing fetus. Even if you eat a healthy, balanced diet, you might not be getting all of the nutrition that you and your baby need. That’s where prenatal vitamins come in. 

Taking a step back, what exactly is a vitamin? It’s a substance that your body is not able to make on its own, so in order to stay healthy, you have to supply it through your diet. That supply can come in the form of vitamin-rich foods, or in the form of supplements—such as prenatal vitamins. You’ll likely be asked at your initial prenatal visit if you’ve started taking prenatal vitamins; ideally, you will have started supplementing one to three months before getting pregnant to help ensure you’ve built up a reserve of vitamins that will be essential to the development of the fetus.  

Prenatal vitamins are specifically formulated to supply the nutrients that you need during pregnancy.

Pregnant women require more folic acid, calcium, and iron than women who aren’t pregnant (we’ll say more on what nutrients to look for in a prenatal vitamin below). 

Without prenatal vitamins, pregnant women can suffer from anemia (not enough red blood cells to supply your body with adequate blood flow), fatigue, muscle cramps, and other health issues. Certain nutrients help babies grow, too—folic acid helps the baby’s brain and spinal cord develop, calcium helps develop baby’s bones, and iron allows your blood to bring oxygen to your baby. During pregnancy, your baby and you draw from the same finite supply of vitamins, and minerals. Prenatal vitamins increase that supply, allowing your body to meet both baby and mother’s combined needs.

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What goes into a prenatal vitamin?

There are a lot of beliefs unsupported by research about what’s healthy for a developing baby, so we’ve tackled this question based on clinical guidelines developed by obstetricians. 

Your prenatal vitamins should include:

  • Calcium: Most calcium in American diets come from milk, yogurt and cheese. It can also be found in spinach, broccoli, and chia seeds as well as bony fish, like sardines. As we said above, calcium helps your baby’s bones form and grow. It also helps the fetus’ blood vessels and muscles function. It is found in two different forms: calcium carbonate and calcium citrate. Calcium carbonate needs stomach acid in order to be absorbed, so it is best taken with meals. Calcium citrate is absorbed with or without food. Be aware of the type you’re taking to determine the best time to take your prenatal vitamin. The recommended amount of calcium during pregnancy is 1000mg daily and it is best absorbed when taken as 500mg twice a day.
  • Vitamin A: found naturally in fish oil, so you probably know people who take it as a daily supplement. It’s essential for your eyes to function well—Vitamin A deficiency is the most common cause for blindness worldwide—and it’s important for many of your body’s other processes such as cell growth and organ health. 
  • Vitamin B1 (Thiamine): helps metabolize carbs.
  • Vitamin B3 (Niacin): allows fats and sugards to metabolize It’s found in a lot of processed foods, so Vitamin B3 deficiencies are rare, but it’s still recommended as a pregnancy supplement in prenatal vitamins.
  • Vitamin B5 (Pantothenic Acid): synthesizes Coenzyme A, which plays a crucial part in energy production. (Coenzyme A’s role in your body is really interesting, but it’s about 5 levels of geeking out beyond the scope of this post, so we’ll spare you the lecture.)
  • Vitamin B6. Another one with complex benefits—trust us, you (and your baby) need it. It can also help treat symptoms of nausea in early pregnancy. 
  • Vitamin B7 (Biotin): Needed forcell growth, fatty acid production, and metabolism. Note: the recommended daily dose of biotin goes up slightly for breastfeeding women.
  • Vitamin B9 (Folic Acid): The synthetic version of Folate often fortified in processed food or as a supplement, this is one of the better-known vitamins. Folic acid helps with the baby’s brain and spinal cord development and helps prevent neural tube defects.
  • Vitamin B12: Another one with an important, but hard-to-describe, function (red blood cell formation and DNA synthesis, to name a few). Fun fact: all forms of this vitamin contain cobalt, the blue chemical element that was used a lot in ancient paintings.
  • Vitamin C: We’ve all turned to Emergenc-C when we’re trying to fight off a cold. Vitamin C deficiency leads to scurvy (remember the sailors?) and the vitamin is essential in cellular metabolism. Our bodies can’t produce or store this, so we need to consume it regularly.
  • Vitamin D: helps your body absorb calcium. Also received through exposure to sunlight, or through fortified milk and fatty fish like salmon. All women, including those who are pregnant, need 600 international units of vitamin D a day. Vitamin E: important for supporting your immune system—vital during pregnancy.
  • Omega-3 Fatty Acids (also known as DHA or docosahexaenoic acid): essential for baby’s brain development. Recommended values are 300mg/d and most women get about 45-115mg of DHA a day. DHA is found in fish, but in pregnancy, women are recommended no more than 2 servings of fish a week, which is why supplementation is necessary. 
  • Iron: essential for oxygen transport for you and the baby. 
  • Choline: growing evidence shows choline improves several pregnancy outcomes and protects against certain neural and metabolic disorders.
  • Zinc: plays an important role in RNA and DNA development and is important for reproductive organ growth. 

The catch—what are the side effects?

Ideally, prenatal vitamins are taken during preconception and throughout all three trimesters of pregnancy. However, some people experience side effects with prenatals—the most common being constipation and nausea (read our other article on Prenatals and Nausea). Iron, in particular, can cause constipation.

It can be hard to tell what’s a side effect of prenatal vitamins and what isn’t, because the early stages of pregnancy can also produce similar side effects.

The goal is to get through at least half of the second trimester when much of the fetal development has happened. 

What you can do about constipation 

For some, constipation in pregnancy is problematic. At the beginning, much of this is influenced by the high levels of progesterone in the body slowing down the intestines, and the iron in prenatal vitamins doesn’t help. Make sure you’re eating a high-fiber diet and drinking plenty of water. Pears, figs, papaya, and prunes are all high in fiber. You can also take over-the-counter fiber supplements and add stool softeners to your daily regimen. 

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And don’t underestimate the power of the Squatty Potty! A footstool on the floor in front of your toilet can change the posture so that you are in a squatting position: an easier position to facilitate bowel movements. My friends know -- I give them as housewarming gifts!

What you can do about nausea 

Many people experience nausea in the first and early second trimester; again, a side effect of the progesterone circulating in the body to support the pregnancy. This can make it even more difficult to swallow a prenatal vitamin. For nausea in early pregnancy, try Natalist's Good Morning Tea made for nausea relief, ginger (in the form of freshly cut ginger, tea, candy, or gum) or Vitamin B6 (pyridoxine) and doxylamine succinate (known as Unisom). Vitamin B6 at 10-25mg orally every 6-8 hours (maximum dose of 200mg/day) can help with nausea. The addition of doxylamine succinate can  enhance the treatment of nausea and vomiting for people that aren’t getting relief from Vitamin B6. Nausea is also improved with small, frequent snacks (carbs may be your best friend!). If the nausea and vomiting persists, talk to your doctor about prescription medication options. 

And, as always—if you’re struggling with the side effects of prenatal vitamins, talk with your doctor about what to do. You might be able to switch vitamins, or find another solution that will help you through the preconception and pregnancy timeframe. 


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