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Can Prenatal Vitamins Cause Weight Gain? The Truth

Medically Reviewed by Caitlin Goodwin, MSN, RN, CNM
Is weight gain a side effect of prenatal vitamins?

Are you currently expecting and worried you’re gaining too much weight too quickly? Do you wonder if your prenatal vitamins could be contributing to your weight gain?

It’s never too early to start taking care of your baby, and a prenatal vitamin will get you both off to a healthy start. But are there any risks associated with prenatal vitamins? Could they possibly cause weight gain or any other side effects?

We will discuss why it’s important to take a prenatal vitamin and when you should start taking one. We’ll also consider whether prenatal vitamins cause weight gain and what to do if you’re experiencing sudden weight gain or other possible side effects from your prenatal vitamins.

Key Takeaways

  • There is no evidence to suggest that prenatal vitamins will make you gain extra weight.
  • Prenatal vitamins are important for proper fetal development and filling nutritional gaps for both mother and baby.
  • Benefits of prenatal vitamins include reduced nausea, fertility boost, and reduced risk of congenital disabilities.
  • Prenatal vitamins should be taken before conception or as soon as a pregnancy is confirmed.
  • Some mothers may experience nausea after taking prenatal vitamins due to the iron content, but this can be managed by splitting the dose or taking it at a different time.

Why Take a Prenatal Vitamin?

Proper nutrition is essential for your health and your baby’s health. Your baby depends on you for all of their nutrition needs, and it’s possible your diet could be lacking the vitamins and minerals needed to support a healthy pregnancy.

Taking a prenatal vitamin will fill those nutritional gaps essential for healthy fetal development. It’s even more important to take a prenatal vitamin if you have any dietary restrictions, health issues, or pregnancy complications (1).

Other benefits of prenatal vitamins include:

  • Reduced nausea: Vitamin B6 has been shown to reduce nausea associated with morning sickness. Women who use prenatal vitamins before conception tend to have less nausea in the first trimester than those who don’t.
  • Fertility boost: Research proves that taking a prenatal vitamin boosts your chances of conceiving a healthy baby faster.
  • Reduced risk of congenital disabilities: The biggest reason to take a prenatal vitamin is to ensure you get enough folic acid. Folic acid drastically reduces the risk of neural tube defects in your growing baby (2).
While it’s true that supplementing with Vitamin B6 reduces nausea, prenatal vitamins do not have the same effect. Many women experience nausea after taking their vitamins due to the iron content in the vitamin (3).

Some mothers cut down on nausea by splitting their vitamin in half and taking it twice a day. Others prefer to take the vitamin after dinner. Some choose to take gummy prenatal vitamins, and others take a low-iron children’s vitamin along with a separate folic acid supplement until their nausea has lessened.

However, switch to a conventional prenatal vitamin after the first trimester because gummy vitamins and children’s vitamins don’t have the iron your body and baby need.

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Editor's Note:

Caitlin Goodwin, MSN, RN, CNM

Can’t I Just Take a Multivitamin?

Prenatal vitamins are specifically formulated to meet your growing baby’s nutritional needs along with your own, whereas a multivitamin will only meet the needs of your body.

Pregnancy increases your daily intake requirement for vitamins and minerals to support proper fetal development. Prenatal vitamins typically provide higher doses of folic acid (folate or folate supplements) which help prevent neural tube defects. They also supply iron, which prevents anemia and supports your baby’s development, and calcium to support bone development.

Most prenatal vitamins also contain DHA (docosahexaenoic acid) to support the development of your baby’s brain, eyes, and nervous system.

When Should I Start Taking Them?

Healthcare professionals recommend starting a prenatal vitamin three months before you conceive to prepare your body to grow a baby. However, we all know pregnancies aren’t always planned. So if you were just surprised with a positive pregnancy test, start taking a prenatal vitamin right away.

Will They Make Me Gain Weight?

There is no evidence that prenatal vitamins make you gain weight. Most pregnant women gain about 25-35 pounds throughout their pregnancy, whether they use a prenatal vitamin or not. And since vitamins contain zero calories, the weight gain is likely due to the pregnancy itself.

The iron in prenatal vitamins can cause constipation and bloating, making your clothes feel tighter. But no one can definitively proclaim them as causing you to gain weight.

When experiencing constipation and bloating, I recommend that moms increase fiber and fluids, but if that’s not enough, they can take docusate sodium.
Headshot of Caitlin Goodwin, MSN, RN, CNM

Editor's Note:

Caitlin Goodwin, MSN, RN, CNM

But Why The Sudden Weight Gain?

If you experience sudden weight gain at any point throughout your pregnancy, visit your doctor as soon as possible. If combined with a severe persistent headache, visual changes, or right upper abdominal pain, this could signify preeclampsia (4).

Preeclampsia is nothing to mess with. It can have severe effects on both you and your baby, such as low birth weight, miscarriage, stillbirth, seizures, and even maternal death.

Other Side Effects of Prenatal Vitamins

There is no way to tell if prenatal vitamins can make you gain weight, but they can cause other minor side effects for some women, such as:

  • Nausea and vomiting.
  • Constipation or diarrhea.
  • Dark stools.
  • Metallic taste.
  • Sleeplessness.
  • Loss of appetite.
  • Bright yellow or green coloration in urine.

However, most of these side effects are symptoms common with pregnancy, so it can be difficult to determine if it is truly the prenatal vitamin causing them. Talk with your healthcare provider about any side effects from taking prenatal vitamins (5).


Do Prenatals Make You More Hungry?

On the contrary, prenatal vitamins cause some women to lose their appetite. While there is evidence that prenatals can make you less hungry, there isn’t any research to support they make you hungrier.

If you’re hungrier than you normally would be, that’s most likely a side effect of pregnancy itself.

Do Prenatal Vitamins Cause Weight Gain When Not Pregnant?

No research has concluded that prenatal vitamins cause weight gain, and this includes taking them while you aren’t pregnant. If anything, prenatal vitamins can cause you not to want to eat because some possible side effects are:

  • Feeling bloated
  • Constipation
  • Nausea
  • Vomiting
  • Loss of appetite

It isn’t recommended to take prenatals when you aren’t pregnant. Prenatal vitamins can cause you to store too much iron if you aren’t pregnant or expecting to be pregnant.

Who Should Not Take Prenatal Vitamins?

While prenatal vitamins are packed with important nutrients for you and your baby, some moms shouldn’t take them.

People who have a disorder that causes their body to store abnormally high amounts of iron shouldn’t take prenatal vitamins because prenatals have higher iron levels than other vitamins. People who aren’t pregnant shouldn’t take them, either.

To Sum it Up

Taking a prenatal vitamin will support your health and your baby’s health. They’ve even been shown to boost fertility, increase iron levels, and reduce the chances of congenital abnormalities. By taking a prenatal vitamin three months before planning to conceive, you will receive enough folic acid, calcium, and iron to support a growing baby.

Although prenatal vitamins can cause constipation, bloating, and other minor side effects for some women, there is no proof they can cause weight gain. Because they contain zero calories, your weight gain is most likely from the pregnancy itself.

Take Note

If you are experiencing sudden weight gain, contact your physician as soon as possible, as this can be a sign of serious pregnancy complications.
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Headshot of Caitlin Goodwin, MSN, RN, CNM

Medically Reviewed by

Caitlin Goodwin, MSN, RN, CNM

Caitlin Goodwin MSN, RN, CNM is a Certified Nurse-Midwife, clinical instructor and educator. She has ten years of nursing experience and enjoys blogging about family travel and autism in her free time.