Want kids one day? Take the quiz
Do you need an iron supplement in pregnancy? Here

Do you need an iron supplement in pregnancy? Here's why it's a key ingredient

5 min read

Iron is the building block of hemoglobin — it's essential for the formation of red blood cells and the proteins in your blood that transport oxygen from your lungs throughout the body.* Whenever blood is in high demand, so is iron.

When is blood in high demand? Many of the situations solely impact people with ovaries, making iron deficiency more common among that population:

  • After significant blood losses, like after delivering a baby, after a heavy menstrual cycle, or after surgery.
  • During times of rapid growth, like when you’re growing a new organ (such as a placenta), and when your uterus is more than doubling in size to make room for a fetus that’s growing rapidly.

To avoid iron deficiency during pregnancy, the American College of Obstetricians and Gynecologists (ACOG), the leading body of OB-GYNs recommends, all pregnant people get 27 mg of iron a day.*

Why is iron so important during pregnancy?

When growing another human, your blood volume expands by 50%, on average, to support the transfer of oxygen across the placenta and for fetal development.* Most of this blood volume expansion occurs later in gestation (in the second and third trimesters) to provide the fetus with more oxygen as they grow — as a result, there's an increased need for iron in the pregnant person to support that transfer of oxygen.* To accommodate this jump in demand, you need to take in almost 50% extra iron: from 18 mg for nonpregnant adults to 27 mg during pregnancy. (The recommended upper limit is 45 mg per day.)

Despite the importance of the nutrient, rates of iron deficiency during pregnancy are extremely high. National health data suggests that many people enter pregnancy already at an iron deficit. While this iron deficiency showed up in only about 5.3% in pregnancies during the first trimester, by the third trimester, 27.5% of pregnant people showed signs of iron deficiency.

Why is iron deficiency so prevalent, in pregnant people and in general?

Low iron is the most common micronutrient deficiency in the world, one that disproportionately afflicts birthing parents and infants.

Here are a few reasons why this might be the case:

  • It’s hard to get enough iron from food. According to ACOG, the typical American way of eating does not provide adequate iron to support needed blood volume expansion during pregnancy. And during pregnancy, increased iron needs further widen the gap between the amount of iron consumed and the amount needed.
  • For anyone with gastrointestinal issues, like irritable bowel syndrome (IBS) or Celiac disease, the ability to absorb iron is diminished.
  • An estimated 10% of people with ovaries have “heavy” menstrual bleeding (defined as >80 mL of blood loss per month). Month after month of heavy bleeding can deplete iron stores. This estimate is likely higher among those who use the copper intrauterine devices (IUDs) for birth control, which are known to increase menstrual bleeding. If you have a history of heavy menstrual bleeding, you might be starting pregnancy already at an iron deficit.

According to leading health organizations, like ACOG, the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO), prenatal screening should be a routine part of prenatal care. People who are iron deficient should make sure they’re getting enough from food and/or dietary supplements.

What are the best food sources for your daily iron intake?

There are two types of iron naturally found in food:

  1. Heme iron, which is the most readily absorbed form of food-based iron (2-3x more absorbable than non-heme iron on average) can be found in:

    • Beef or chicken liver
    • Red meat and poultry
    • Organ meats
    • Oysters, clams, and mussels
    • Canned sardines
    • Canned tuna
  2. Non-heme iron, the more challenging form of food-based iron to absorb, can be found in plant-based foods like:

    • Beans
    • Lentils
    • Spinach (cooked)
    • Potatoes with skin
    • Fortified breakfast cereals and enriched rice or bread
    • Nuts and seeds
    • Tofu
    • Legumes
    • Avocado

Should you take an iron supplement for pregnancy?

Even for those without iron deficiency, ACOG recommends taking prenatal vitamins with iron (along with eating iron-rich foods) to help you hit that full daily requirement of 27 mg.

When do you need to start increasing your iron intake? The general recommendation from ACOG is to start taking prenatals a month before conception, and the CDC recommends getting your daily levels of iron to 27 mg starting at 12-weeks gestation.

The Modern Fertility Prenatal Multivitamin was designed so you can keep taking it long term. Instead of the full 27 mg, it includes 18 — that way, it's balanced enough to take it before, during, and after pregnancy. You can pair the iron in the Prenatal Multi with iron-rich food sources to meet the daily requirement of 27 mg for pregnancy.

Let's talk about iron absorption

The first step is making sure you're getting enough iron every day. Once you've got that covered (through food and/or supplements), it's important to know how to get the most out of your iron intake.

There's a long list of obstacles that impair your absorption of iron, including:

  • Minerals like calcium, phosphorus, and magnesium (found most abundantly in dairy products, as well as in many multivitamins)
  • Tannins (found in coffee and tea)
  • Compounds called phytates and oxalates (found in whole grains, beans, legumes, and even some veggies like spinach)

But there's an additional nutrient that can actually help you improve absorption of iron. Here are three ways you can use vitamin C boost your iron absorption:

  • Pair iron with vitamin C from fresh fruits or vegetables. For example, cook lentils or spinach with tomatoes as a source of vitamin C, or eat an orange with your meal.
  • Separate your source of iron from dairy, coffee, or tea. If you enjoy your morning caffeine jolt and/or you have milk or yogurt at breakfast, you’ll want to take your source of iron later in the day, ideally at least an hour later.
  • Take any iron supplements between meals with liquids other than coffee, tea, or milk.

Fun fact: Studies show that cooking in cast iron imparts iron into your food. If you’re concerned about your iron status, you don’t want to rely on this intervention alone, but it certainly can’t hurt!

What's the deal with iron supplements and GI side effects?

Complaints of GI side effects, like constipation, heartburn, and nausea, are extremely common with iron supplements. Since supplemental iron can be hard for the body to absorb, what's left might break apart and cause disruption to the acidity and microbiome of the gastrointestinal tract.

For many, taking a different form of iron can ameliorate these issues. While research shows pregnant women who took iron in the form of ferrous fumarate or ferrous sulfate complained of the most symptoms, ferrous bisglycinate is associated with the fewest.

The Modern Fertility Prenatal Multivitamin includes 18 mg (the level set by the FDA for pre-pregnancy) of ferrous bisglycinate to minimize uncomfortable side effects.* It also has vitamin C, a nutrient shown to improve the absorption of any iron you're already getting.* When paired with iron-rich eating, the Prenatal Multi can help you meet your daily iron needs while keeping things easy on the tummy.

Ultimately, as long as you stay well below the safe upper limit of 45 mg per day and you tolerate it well, iron supplementation is likely to help ensure you and your future kid are set up for optimal health.*

The Modern Fertility Prenatal Multivitamin

If you're prepping your body for pregnancy or you're already pregnant, the Modern Fertility Prenatal Multivitamin is a science-backed way to get those essential nutrients (including iron, as  ferrous bisglycinate) on board.

The Prenatal Multi:

  • Is packed with 12 essential nutrients recommended by OB-GYNs
  • Was designed for before, during, and after pregnancy
  • Is easy to digest to keep your tummy happy
  • Comes with a reusable glass jar to keep your subscription sustainable
  • Is vegetarian, gluten-free, and has zero preservatives

Start prepping your body now for pregnancy whenever with the Modern Fertility Prenatal Multivitamin.

This article was medically reviewed by Dr. Jenn Conti, MD, MS, MSc.

*This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Did you like this article?

Anna Bohnengel, MS, RD, LD

Anna Bohnengel, MS, RDN, LD is a registered dietitian helping women take control of their fertility. Learn more at www.fertility-nutritionist.com/actionplan. Instagram: @MyFertilityNutritionist

Join the Modern Community

This is a space for us to talk about health, fertility, careers, and more. All people with ovaries are welcome (including trans and non-binary folks!).

Recent Posts

Why does vaginal lubrication matter for sex?

Lube 101: what it is, why to use it, and how to choose the best lube for you

What every female athlete should know about exercise and reproductive health

The Modern guide to ovulation predictor kits and ovulation tests

How to choose the right birth control for you