Why is Iron So Important in Pregnancy?

Figuring out which supplements to take and how much during pregnancy can be a confusing process. Dr. Mare explains why iron is one of the most important supplements to make sure you’re getting.

By Dr. Mare Mbaye

Figuring out which supplements to take and how much during pregnancy can be a frustrating process. With so many options out there, how do you know what’s most important? We've already been over what to look for in a prenatal vitamin, now let's focus on one of the vital minerals needed for a healthy pregnancy, iron.

As a refresher, iron is used to make hemoglobin, a protein that red blood cells use to transport oxygen in the body. Hemoglobin binds oxygen in the lungs and carries it to all the tissues in the body, including to a developing fetus. Blood volume increases due to the demands of pregnancy, making iron a hot commodity during this process. Pregnant people need about double the amount of iron as a non-pregnant person. And since these physiologic changes start very early on in pregnancy (before most women know they are pregnant), it’s important to start supplementation as early as possible when it’s indicated.

Anemia, the most common blood abnormality

Anemia, the most common blood abnormality, is diagnosed when a patient has a lower than normal hemoglobin count. The two most common causes of anemia in pregnancy are iron deficiency and acute blood loss at the time of delivery. We test for anemia via a simple lab draw (a complete blood count) at the very first prenatal visit and again at the beginning of the third trimester. You are considered anemic if your hemoglobin is less than 11 g/dL in the first or third trimesters and 10.5 g/dL in the second trimester.

A study in 2017 found that anemia in pregnancy affects up to 12% of people. The study also revealed that it is much more prevalent in non-Hispanic black women (24%) than in their non-Hispanic white counterparts (3%) during pregnancy. Out of all groups, regardless of race, teenaged mothers had the highest prevalence of anemia in pregnancy. In patients with moderate to severe anemia, we tend to recommend iron supplementation on top of the iron that’s already in prenatal vitamins because we’re starting at such a low number. 

The reason we worry about iron deficiency anemia during pregnancy, specifically, is its association with an increased risk of low birth weight, preterm delivery, and perinatal mortality. There may also be an association between maternal iron deficiency anemia and postpartum depression.

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How do I know if I am low in iron?

Risk factors for iron deficiency anemia in pregnancy include a diet poor in iron-rich foods and/or iron absorption enhancers; a diet rich in foods that diminish iron absorption; pica (eating non-food substances like clay or laundry starch); gastrointestinal diseases that affect absorption; short interval between pregnancies; heavy periods between pregnancies; and blood loss at delivery that is higher than normal for an uncomplicated vaginal or cesarean delivery.

Symptoms of anemia can include fatigue, weakness, fast heart rate, difficulty concentrating, shortness of breath, pale skin, lightheadedness, and cold hands and feet. Talk to your doctor if these symptoms appear. 

If you are diagnosed with anemia, there are plenty of ways to increase your iron stores. The daily recommended dose of iron supplementation during pregnancy is 27 mg, which is found in most prenatal vitamins.

How to increase iron in pregnancy

It is also totally reasonable to increase your iron naturally (so long as you’re not starting at a very low level). One thing to keep in mind while doing so, though, is that there are two types of irons: heme and nonheme iron. Heme iron is the type our body absorbs best. Nonheme iron is the other type, which is best absorbed when eaten with iron absorption enhancers.

Foods that contain heme iron include clams, oysters, liver, beef, and other lean red meat, shrimp, fish, and poultry. You can find nonheme iron in foods such as beans, dark leafy greens, dried fruit, enriched cereals, and lentils. Iron absorption enhancers to pair with your nonheme options include orange juice, grapefruit, strawberries, kiwi, melon, broccoli, tomatoes, and peppers.

It’s also important to watch for any foods you eat that may decrease iron absorption. Try to avoid dairy and soy products, spinach, coffee, and certain teas.

For those who don’t respond well to oral iron supplementation, whether natural or in pill-form, a workup for other causes of anemia may be warranted. If your hemoglobin is very low (especially close to the time of delivery) or you cannot tolerate iron supplements, your doctor may suggest coming in for a few extra appointments to receive iron through an IV or via injections. These methods are excellent at raising iron levels within 2 weeks, but in the long term are comparable to oral supplements.

Whichever method you choose, the important thing is that you are getting the iron you and your baby need. 

For more information about iron and pregnancy, read our article Pregnancy and Iron Deficiency.