Iron is a bit of a hot topic in pregnancy nutrition, because a woman’s need for Iron in pregnancy goes up rather substantially! Iron is a tricky mineral though, because absorption is finicky, supplements tend to make us constipated, and a lot of women end up with food aversions that make things like liver or meat seem really unappetizing. So what’s a girl to do?

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First, Why is Iron so important in pregnancy?

Over the course of the entire pregnancy, a woman will need a little more than 1000mg1,2 of additional Iron ABOVE her regularly needed intake. That’s a lot of Iron! Where does this 1000mg go?

Iron needed for Amount (mg)
Total cost of pregnancy
Fetus 270
Placenta 90
Expansion of red blood cell mass 450
Obligatory basal losses 230
Sum 1040
Maternal blood loss at delivery 150
Total cost 1190
Net Cost of pregnancy
Contraction of maternal red blood cell mass -450
Absence of menstruation during pregnancy -160
Subtotal -610
Net Cost 580

(Table 12)

Translation: To cover the Iron requirements for the fetus, placenta, mom’s increased red blood cells, and the Iron lost at delivery, we need a total of 1190mg of Iron! However, the net Iron we need is actually closer to 580mg once we factor in the breakdown of those extra red blood cells after pregnancy and the fact that we’re not menstruating while pregnant.

It’s easy to assume that the need for this extra Iron is equally spread out over the duration of the pregnancy, but that’s not actually the case. In the first trimester, our need for Iron actually decreases a bit, since menstruation stops and the fetus and placenta aren’t requiring a whole lot yet. Once a woman hits the second trimester though, the need for Iron increases, and continues to increase for the duration of the pregnancy.2

We enter pregnancy with different needs already

It makes sense that if you enter pregnancy already having decent stores of Iron, that you’ll have an easier time keeping your Iron status up during pregnancy. While having suficient Iron stores is more common in the U.S. than in developing countries,  Iron deficiency is still more common than you might think. “Approximately 12 percent of women in the United States enter pregnancy with low or no iron stores, and 18 percent have iron deficiency during pregnancy.”1 Rates are higher in low-income women and women who have had two or more pregnancies.

If iron deficiency progresses to anemia, known as Iron Deficiency Anemia (IDA), then we start to see some adverse effects. If a woman already has IDA when she becomes pregnant, it increases the risk of preterm delivery and a low-birthweight infant by two to three times!1,3 At age 5, these children tend to have lower scores on intelligence, language, gross motor, and attention tests.1,4 Since infants store up iron while in utero to use over their first few months of life, the preterm babies are at risk for iron deficiency in infancy because they haven’t been able to build up their own stores.

Thus, if you’re considering becoming pregnant, it can be a good idea to keep an eye on your Iron before you conceive.

How do we test for iron status?

Typically, iron status can be tested for using standard blood tests for hemoglobin and other iron-containing markers in the blood. Something that makes the interpretation of the levels a bit interesting in pregnancy is the fact that our blood volume increases so much when we’re pregnant. The actual amount of red blood cells increases about 30%, but the plasma volume of our blood increases 50%! “The higher increase in plasma volume compared to red cell mass makes it appear that amounts of hemoglobin, ferritin, and red blood cells have decreased. They have not decreased but rather have become diluted.”1

Thankfully, labs know that this effect needs to be taken into consideration when interpreting results of bloodwork. The following are hemoglobin cut-off values for IDA in pregnancy based on the week of gestation.1

Gestational Week Hemoglobin (g/dL) cut-off for anemia in pregnancy
12 <11.0
16 <10.6
20 <10.5
24 <10.5
28 <10.7
32 <11.0
36 <11.4
40 <11.9

Ferritin, which is the storage form of iron, can also be measured in blood tests. Normal values are >35 ng/mL, depleted (low) stores show up as values <20ng/mL, and Iron Deficiency is considered 15ng/mL or less.

*Note: There are many tests for iron, and the diagnosis for IDA shouldn’t be made on any one test alone. It is best for several tests to be used together to make the diagnosis. (Though this is obviously a doctor’s job, so don’t go diagnosing yourself or thinking I’m diagnosing anything!)

Recommendations for Iron intake and supplementation in Pregnancy

The body is pretty darn smart. Women who have low or deficient iron stores absorb more of their ingested Iron than someone who already has adequate stores. The body is basically saying “I need MORE Iron over here!”

Still, absorption of Iron isn’t exactly high. If you have adequate stores already, you only absorb about 10% of the Iron you ingest. Someone with IDA will absorb about 40% of their ingested Iron.1 When it comes to pregnancy specifically, it’s been realized that Iron absorption rates change as pregnancy progresses. Iron absorption decreases in the first trimester, and then increases in the second and third trimesters.2

In order to make sure that we’re absorbing enough Iron to meet the additional needs of pregnancy, the general recommendation is for women to take a 30mg Iron supplement every day after the first trimester. (By the way, Iron supplements need to be taken separately from other multivitamins in order to maximize absorption.)

However, blanket recommendations aren’t always appropriate (duh, right?). So it’s pretty common for doctors to test a woman’s Iron levels (by Hemoglobin, Ferritin, and other Iron tests) before recommending a supplement. If Hemoglobin is <11g/dL or ferritin is <30ng/mL, then the 30mg supplement is a good idea. If a women’s values are already adequate, then she may not need supplemental Iron.1 Studies haven’t shown a health benefit to the mother or child in that case.

It’s also possible to have too much Iron, though it’s less common than too little. Excessive Iron, seen as hemoglobin values over 13g/dL, can lead to similar negative outcomes as Iron deficiency: low birthweight and premature infants. “In fact, the incidence of these negative consequences increases dramatically when women’s Hb levels, at sea level, are below 95 to 105 g/L [9.5-10.5g/dL] at any time in pregnancy or above 130 to 135 g/L [13.0-13.5 g/dL] after mid-pregnancy.”5

Moral of the story: there is a sweet spot for Iron status. Not too much, not too little. Supplementation should therefore be used with discretion, and under doctor’s orders.

Some women really don’t like Iron supplements because they can be difficult to tolerate. The Iron that isn’t absorbed stays in your digestive tract, and free Iron in the digestive tract and cause some GI side effects like constipation, cramps, and nausea. These side effects tend to increase as the supplement dose goes up.

Getting Iron in your diet

A non-pregnant woman’s recommended daily intake for Iron is 18mg per day. In pregnancy, that jumps to 27mg per day! It can be tough to reach that amount, particularly when the need increases a lot toward the end of the pregnancy. However, in developed countries, like the U.S. it can be possible.

Here are some good sources of Iron in various foods, though this is certainly not an all-encompassing list!6

1c fortified oatmeal = 14mg
3oz oysters = 7.8mg
3oz liver = 5.5mg
1/2c dried apricots = 3.8mg
1/2c lentils or white beans = 3.3mg
1/2c cooked spinach = 3.2mg
3oz lean beef = 2.8mg
1/2c soy beans = 2.3mg
3oz lamb = 2mg
3oz pork or chicken = 1mg

Want my FREE 1-page Printable Pregnancy Nutrient Cheat Sheet, including Iron, Folate, DHA, and more? [thrive_2step id=’709′]Click here[/thrive_2step] to get it!

A few notes:

I had no idea oysters were so high in Iron until I started writing this post. I also was under the impression that chicken had more Iron in it than it does. Always learning something new! It helps to have an idea of how much is in some of your favorite foods, so you can have an idea of whether or not you’re anywhere close to the 27mg recommendation.

If you want to look up the content of a nutrient in any particular food, check out the USDA’s Nutrient Database. It’s where I got all of the information for the above Iron details, as well as everything on the spiffy printable I linked to above! They even make it possible to create a Nutrient Report for any nutrient. This means you could actually create a PDF of ALL of the foods in the database ranked by the amount of Iron (or any other nutrient) in them. I didn’t do that here because it ends up being an amazingly long list, so I just pulled out a few that seemed like ones most people would eat. But take a look and see if any of your other favorite foods have a good amount in them!

Many cereals and breads are fortified with Iron (just keep in mind that the Daily Value is not based on the 27mg needed in pregnancy, but the 18mg a non-pregnant woman needs). Fortified items are a great way to ensure you’re getting the Iron you need.

Plant sources of Iron aren’t as well absorbed as heme sources found in meats and seafood, but Vitamin C can help to enhance the absorption of the non-heme Iron. Therefore, it’s a good idea to pair those sources with foods higher in vitamin C.

The Take-Away:

As with any specific nutrient recommendation, it’s best to talk to your doctor about any questions that you have. I simply wanted readers to be aware that Iron is important in pregnancy, and to know of some ways that you can work on reaching the recommended amount of intake. I hope this post was helpful for all my pregnant mamas out there!

Sources

  1. Brown JE. Nutrition Through the Lifecycle. 5th ed. Cengage Learning; 2014.
  2. Bothwell TH. Iron requirements in pregnancy and strategies to meet them. Am J Clin Nutr. 2000;72(1 SUPPL.). doi:10.3389/fphar.2014.00155.
  3. Allen LH. Biological Mechanisms That Might Underlie Iron’s Effects on Fetal Growth and Preterm Birth. J Nutr. 2001;131:616-635.
  4. Tamura T, Goldenberg RL, Hou J, et al. Cord serum ferritin concentrations and mental and psychomotor development of children at five years of age. J Pediatr. 2002;140(2):165-170. doi:10.1067/mpd.2002.120688.
  5. Jp P, Lm D, Mn G, Dowswell T. Daily oral iron supplementation during pregnancy ( Review ). 2015;(7). doi:10.1002/14651858.CD004736.pub5.www.cochranelibrary.com.
  6. USDA Food Composition Databases. https://ndb.nal.usda.gov/ndb/search/list. Accessed January 1, 2016.

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