The Critical Role of Iron in Pregnancy: What Every Expectant Parent Should Know

Written by: Maggie Assaff, RD

Iron is one of the most important nutrients during pregnancy — yet it’s also one of the most common deficiencies. Many women experience low iron levels by the second or third trimester, which can leave them feeling tired, dizzy, or even short of breath.

As a registered dietitian specializing in women’s health, I often see clients wondering:

“Do I need an iron supplement?”

“Does my prenatal vitamin already have iron and is that enough?”

“And why do some iron pills make me feel nauseous?”

Let’s break it all down — what iron does, why your needs increase in pregnancy, and how to make sure you are getting enough from food and supplements to support a healthy pregnancy.

Why Iron Matters (Especially Mid-to-Late Pregnancy)

Iron is crucial throughout pregnancy, but especially in the second and third trimesters, when your blood volume expands rapidly, doubling nearly 50%,  and your baby is growing the fastest.

During pregnancy iron helps to:

• Carry oxygen to you and your baby

• Support the placenta

• Support your baby’s brain development and build their iron stores¹

Your baby relies heavily on your iron levels—most of their stored iron (what they use for the first 4–6 months of life) is built during the last trimester.

How Much Iron Do You Need?

According to Canadian dietary references, pregnant women’s iron needs increase to 27 mg of iron daily². That’s almost double what non-pregnant adults need. 

It’s important to focus on an iron-rich diet and take your prenatal vitamin to meet your needs. A daily prenatal supplement with 16 - 20 mg of iron is recommended during pregnancy¹. When combined with iron taken from the diet, this typically provides adequate iron for a healthy pregnancy. 

If your bloodwork shows low iron, your healthcare provider may suggest an additional iron supplement on top of your prenatal.

What Happens When Iron Levels Are Low?

Low iron, or iron-deficiency anemia, can occur in pregnancy because needs are higher and some women may not eat enough iron-containing foods or may choose foods in which iron is less easily absorbed^1,3. Not getting enough iron can lead to: 

• Fatigue

• Dizziness or shortness of breath

• Trouble concentrating

• Increased risk of preterm birth or low birth weight

• Lower iron stores in your baby at birth

Because symptoms can be subtle, prenatal bloodwork is important for catching low iron early.

Best Food Sources of Iron

Although your prenatal vitamin will provide you with added iron, it is still important to include a variety of iron rich foods in your diet. There are two types of iron found in food:

• Heme iron (animal sources, better absorbed)⁴:

  • Lean red meats (beef, lamb)

  • Poultry (chicken, turkey)

  • Fish and shellfish

  • Eggs

• Non-heme iron (plant sources, less easily absorbed)⁴:

  • Legumes (lentils, chickpeas, beans)

  • Tofu and other soy products

  • Dark leafy greens (spinach, kale)

  • Seeds (pumpkin, hemp)

  • Fortified cereals and whole grains

Aim to have 1-2 servings of iron-rich foods with each of your meals.

Pro tip: To maximize absorption of non-heme iron, pair iron-rich foods with vitamin C–rich foods (think citrus fruits, bell peppers, strawberries, tomatoes) and avoid pairing iron-rich foods with coffee, tea, or calcium-rich foods at the same time.

When to Consider an additional Iron Supplement

If you’re eating well but still struggling with fatigue, lightheadedness, or your lab results show low

iron, your health care provider may recommend an additional iron supplement. 

Supplementation may be needed if:

• Your doctor or midwife informs you that your iron levels are low

• You have a history of heavy periods or anemia before pregnancy

• You’re expecting multiples

• You follow a vegetarian or vegan diet

Tip to maximize iron absorption: 

• Take your iron supplement at a different time of day than your prenatal or calcium supplement

• If tolerated take it on an empty stomach with a source of vitamin C such as, a glass of orange juice, peice of citrus fruit, strawberries, or 100-200 mg vitamin C supplement

• and space it 1-2 hours away from coffee, tea, or calcium-rich foods/supplements 

Managing Side Effects of iron supplementation

Digestive issues are common, but there are ways to reduce them^1,5:

✅ Choose gentle forms like bisglycinate

✅ Try taking your supplement with a meal or before bed

✅ Stay hydrated and include fiber-rich foods in your diet to help with constipation

✅ Split the dose into two smaller amounts if recommended by your provider

Key Takeaway

Iron supports both you and your baby’s health, ensuring proper oxygen transport, energy, and development. Deficiency can cause fatigue and complications, but the right supplement — at the right dose — makes a world of difference.

If you’re unsure which product is right for you, or if your prenatal vitamin provides enough iron, speak with a registered dietitian. We can help you interpret your blood results, recommend gentle supplement options, and guide your diet to optimize absorption.

Interested in Personalized Prenatal Nutrition Support?

Every pregnancy is unique — and your nutrition plan should be too. If you’re feeling unsure about your iron needs, wondering whether your prenatal vitamin is enough, or want guidance on choosing the right supplement, partnering with a prenatal nutrition expert can make all the difference.

As registered dietitians specializing in pregnancy nutrition, we can help you:

• Understand your bloodwork and iron levels

• Choose iron supplements that are gentle and effective

• Build a daily meal plan that supports ideal iron absorption

• Reduce common pregnancy symptoms like fatigue and constipation

• Feel confident that you’re supporting your baby’s growth and development

✨ If you’re pregnant and want to optimize your nutrition, we invite you to schedule a session with one of our prenatal nutrition registered dietitian. Whether you’re in your first trimester or nearing birth, we’re here to support you every step of the way.

Click here to book your prenatal nutrition session and get personalized guidance you can trust.

References

1. Health Canada. Prenatal Nutrition Guidelines for Health Professionals – Iron Contributing to a Healthy Pregnancy. 2019.Retrieved from https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/fn-an/alt_formats/hpfb-dgpsa/pdf/pubs/iron-fer-eng.pdf 

2. Health Canada. (2023, December 18). Dietary reference intakes tables: Overview. Government of Canada. Retrieved from https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables.html

3. Sunnybrook Health Sciences Centre. (n.d.). Iron deficiency & supplementation in pregnancy. Retrieved from https://sunnybrook.ca/content/?page=iron-deficiency-supplements-pregnancy

4. Unlock Food. (2019, September 8). How to get more iron from food. EatRight Ontario. Retrieved from https://www.unlockfood.ca/en/Articles/Vitamins-and-Minerals/How-To-Get-More-Iron.aspx

5. Association of Ontario Midwives. (2025, July). AOM Iron cost chart [PDF]. Retrieved from https://www.ontariomidwives.ca/sites/default/files/Poverty/AOM%20Iron%20cost%20chart.pdf