Do Prenatal Vitamins Cause Weight Gain? Or Am I Safe To Go Ahead?

Women expect to gain weight when they become pregnant, but many wonder if their weight gain is more than just a baby on board. It’s recommended that women put on anywhere between 25 to 35 pounds  when pregnant, adding a mere 300 extra calories to their diet.

What happens if mom-to-be is doing this and still finds herself gaining too much, too fast?

Women often connect the addition of a prenatal vitamin to their diet with the beginning of weight gain woes, and this has led many to think that the former is causing the latter.

Women are told to take a good prenatal vitamin to ensure their children get the necessary nutrients in the womb, and many of us even start ingesting them the minute we start trying to conceive – some of us even way before that, too.

Due to all the confusion about what prenatal vitamins are and aren’t capable of, we’re going to discuss why they are necessary, what they contain, why many women swear they make them put the pounds on even faster, and whether or not prenatal vitamin intake is connected to weight gain during pregnancy at all.

Why Take a Prenatal Vitamin?

There’s an ongoing debate about the effectiveness of prenatal vitamins.

Folic acid is an absolute must and added vitamin D and iron are also essential to a baby’s development.

A lack of folic acid in the early days of pregnancy has been linked to increased risks of neural tube defects, such as spina bifida1.

Kids Health points out that these defects, which affect the brain and spinal cord, happen as early as the first month of a woman’s pregnancy, and eating foods with folic acid may not be enough to ensure she has enough of these nutrients to support the baby.

There are also those who argue that simply taking extra vitamin D and folic acid is enough, but the well-roundedness of a multi-vitamin suits many moms.

It’s fun to pretend that we’re going to eat all healthy food and cover all of our nutritional needs in our diets, but pregnancy doesn’t always make that easy.

Food aversions, morning sickness, and insane cravings make consuming all the right foods every day for the baby’s health difficult, and leaning on a prenatal vitamin ensures plenty of folic acid, vitamin D, and every other vitamin a child might need for proper development2.

Can Prenatal Vitamins Cause Weight Gain?

Prenatal vitamins are great at all of the following:

  • Adding folic acid, iron, and vitamin D for mom and the baby
  • Offering an overall umbrella of nutrient help
  • Offering mom thick, beautiful hair
  • Sometimes clearing up mom’s complexion.

What a prenatal vitamin cannot do, though, is make mom put on weight. So, the answer to that question is a big NO. Those added nutrients from a prenatal vitamin do not come in the form of added calories, and excessive caloric intake beyond the number of calories a body burns in a day’s time is what causes weight gain3.

What’s Making You Fat Then?

The obvious answer to why we gain when pregnant is the baby.

The problem is that many women feel the prenatal vitamin somehow adds to the weight gain or makes it worse, but that’s just your mind playing tricks on you.

While prenatal vitamins cannot cause weight gain in the conventional way, they can mimic the symptoms.

  • Constipation occurs when you don’t have regular bowel movements. Constipation can be uncomfortable and make mom feel like she is heavier than normal. The added iron in prenatal vitamins makes them a culprit for causing constipation4.
  • Bloating often occurs because of constipation. You may start showing earlier than usual, where your stomach may look like you are in the second trimester when you are still in the first. All of the backed-up stool that refuses to move causes the bloating.

How To Fix The Problem

There are ways to deal with iron causing uncomfortable bloating. A nutritionist writing for The Bump suggests:

– Go for fiber. Adding some leafy greens, colorful veggies, and yummy fruit should do the trick.

– Add water. Water helps everything in the body move, and without water the fiber won’t be able to effectively do its job. Here’s an article where we talk about how much water you should be drinking while pregnant.

– Check out the prenatal vitamin label. Iron is needed when you’re pregnant, but the amount varies. Someone who is anemic will need more, but someone who is not may be able to switch to a prenatal vitamin that doesn’t contain as much iron. This can help solve the bloating problem.

– Talk to your doctor about a very mild stool softener to get things moving again. Don’t ever add new medications or vitamins without doctor’s approval, but do see if they can recommend a safe way to rid the body of excess stool to stop bloating.

Other Weight Gain Issues

No research to this date has shown that there is any direct link between consuming prenatal vitamins and gaining weight. Women can take them when they are pregnant or when they are trying to conceive, and weight changes can’t be pinned on them.

The indirect links related to constipation or bloating could also happen if you take any extra iron-containing vitamin, since iron is known for backing up the bowels.

Constipation is also a common complaint among pregnant women since digestion is slower during this time. In fact, a woman can experience constipation simply because of pregnancy without the prenatal vitamin being involved at all5.

However, it is wise to be aware of when weight gain seems to be careening out of control during any stage of pregnancy, and talking to your doctor about it.

Blaming the prenatal vitamin is a mistake as it can cause mom to miss other more serious reasons for putting on excess weight quickly, and being overweight/obese during pregnancy is a very dangerous problem.

Fluid retention is a normal part of pregnancy that may also cause mom to put on the pounds.

It’s not a serious problem most of the time, but it can be in certain circumstances.

Fast weight gain, especially connected to fluid retention, can be a sign of a blood clot or preeclampsia.

Wrapping It Up

Prenatal vitamins cannot cause weight gain in the conventional way, and they are important for a healthy pregnancy and baby. They don’t cause mom to add more calories to her diet. However, they can cause bloating, making mom feel heavier than she’s used to.

Stay on the prenatal vitamin but talk to a doctor about any weight gain that feels excessive.

A doctor or midwife can assess your unique situation and help create a plan moving forward that will ensure you gain enough just enough weight you need to put on when expecting a little bundle of joy, but not so much that complications occur due to the extra pounds.


  1. Folate and neural tube defects. Accessed June 21, 2019.
  2. Vitamin D And Pregnancy. Accessed June 21, 2019.
  3. Prenatal Vitamins.,143927/. Accessed June 21, 2019.
  4. Prenatal vitamins: Why they matter, how to choose. Accessed June 21, 2019.
  5. 5 Safe Remedies for Constipation in Pregnancy. Accessed June 21, 2019.

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Medically Reviewed By: Christine Traxler M.D.

Medically Reviewed By: Christine Traxler M.D.

Christine Traxler MD is a retired family practice physician and graduate of the University of Minnesota School of Medicine in 1986. She has worked with patients in rural Minnesota for two decades.

She has written several books on medical topics, and has extensive experience caring for women of childbearing age, women in pregnancy, and menopausal women.

As a writer and editor, she specializes in writing coursework for medical students and other healthcare providers, with a predominance of writing on general medical topics and premedical scientific topics.

She has more than a decade of experience in the writing field, having written books on dermatology, medical assisting, nursing, and pregnancy.

She has written thousands of articles for laypeople and professionals alike on a variety of medical subjects.

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