Iron deficiency in pregnancy

Photo of pregnant woman taking tablets

Pregnant women often develop anemia due to a lack of iron (iron deficiency). Then it's a good idea to take iron supplements. In women who have normal iron levels, taking iron supplements as a precautionary measure probably doesn’t have any health benefits. They can usually get enough iron in their diet.

Iron is a mineral that is found in many proteins and enzymes that the body needs in order to stay healthy. Most of the iron in our bodies is found inside hemoglobin, the pigment in red blood cells. Hemoglobin transports oxygen to all of the tissues and organs in the body. If there isn’t enough iron in the blood, the amount of hemoglobin in the blood decreases too. This can reduce the oxygen supply to cells and organs.

Low levels of hemoglobin are also known as anemia. If these low levels are caused by a lack of iron, it is called iron deficiency anemia. Pregnant women need more iron overall, so they are more likely to develop iron deficiency anemia.

What are the consequences of iron deficiency in pregnancy?

Iron deficiency anemia can make you feel tired and exhausted. Severe anemia can lead to complications in pregnancy. For instance, it can weaken the woman’s and make infections more likely. It also increases the risk of the baby weighing too little at birth (low birth weight). Mild anemia generally doesn’t affect the child, though.

Severe anemia is rare in healthy pregnant women who eat a balanced diet. But anemia can cause serious health problems in women who don’t, or can’t, eat a balanced diet.

According to German health authorities, pregnant or breastfeeding women need 20 to 30 milligrams (mg) of iron per day. It can be particularly difficult for vegetarians to get that amount of iron in their diet alone.

How is anemia diagnosed?

Women have several blood tests during their check-up appointments in pregnancy. In this way, iron deficiency anemia can be detected early on and treated using iron supplements.

At the start and towards the end of pregnancy, hemoglobin levels above 11 grams per deciliter are considered to be normal. Between three and six months of pregnancy, a small drop to 10.5 grams per deciliter is also considered to be normal. If a woman's hemoglobin levels are lower than this, the iron levels in her blood are measured too. This can help to determine whether her low hemoglobin levels really are due to a lack of iron.

Because the body can store a certain amount of iron, the ferritin levels in the blood are measured too. This shows how full the body's iron stores are. If someone’s iron stores are empty but their hemoglobin levels are still normal, they are said to have latent (hidden) iron deficiency.

Which foods have iron in them?

We normally get iron in the food we eat. Meat has a lot of iron in it, from hemoglobin in the animal’s body. Liver is particularly high in iron.

It is harder for the body to use the iron from plant-based foods. But some plants are good sources of iron too. These include cereals, for instance in the form of whole grain flakes (breakfast cereals), and legumes such as lentils and beans. Green leafy vegetables like lamb’s lettuce and spinach, and herbs like parsley and cress, also have some iron in them.

Illustration: Iron-rich foods

Iron-rich foods

Iron can be taken as dietary supplements too. These are available without a prescription in the form of tablets and drops.

When does it make sense to take iron supplements?

Iron supplements are particularly suitable if someone has iron deficiency anemia. Then the doctor usually prescribes high-dose iron supplements. You take these supplements every day or every few days, depending on how severe your iron deficiency is.

Iron can also be given through a drip (infusion). But this is only recommended if your body can't absorb enough iron in the bowel.

Do women with normal iron levels benefit from taking iron supplements?

Pregnant women with normal iron levels in their blood are sometimes advised to take iron supplements in order to prevent anemia. A lot of pregnant women take these supplements because they think their bodies need more iron during pregnancy.

A group of researchers summarized the results of more than 60 studies on the use of iron supplements in pregnancy. A total of more than 40,000 women took part in the studies. The results show that, if women have normal iron levels, taking 30 mg of iron per day as a precautionary measure doesn’t have any noticeable health benefits for them or for their children. Although the iron supplements reduced the risk of anemia, they didn’t influence the number of preterm births, the number of babies with a low birth weight (under 2,500 grams) or infections in pregnant women.

Side effects and dose

When it comes to iron intake, finding the right balance is key. It is not only too little iron that can cause problems – too much iron can be unhealthy too. Although our bodies can store a certain amount of extra iron, higher-dose iron supplements may cause gastrointestinal (stomach and bowel) problems like constipation, nausea, vomiting and diarrhea. When taken on an empty stomach, they can damage the lining of the stomach.

Some experts recommend only taking iron supplements once or twice a week rather than every day – but at a higher dose (such as 120 mg). Research has found that iron supplements can still prevent anemia when taken only once a week. The idea is that taking iron supplements less often will enable women to take them for longer, and reduce the likelihood of side effects. But it’s not clear whether that's really the case.

Keep iron supplements out of children’s reach

Like all medications, iron tablets should be kept in a place where children can't get to them. Even if iron is “only” a natural mineral, an accidental overdose can be life-threatening for children.

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Gesellschaft für Pädiatrische Onkologie und Hämatologie (GPOH). Eisenmangelanämie (S1-Leitlinie). AWMF-Registernr.: 025-021. 2021.

Peña-Rosas JP, De-Regil LM, Garcia-Casal MN et al. Daily oral iron supplementation during pregnancy. Cochrane Database Syst Rev 2015; (7): CD004736.

Peña-Rosas JP, De-Regil LM, Gomez Malave H et al. Intermittent oral iron supplementation during pregnancy. Cochrane Database Syst Rev 2015; (10): CD009997.

Rogozinska E, Daru J, Nicolaides M et al. Iron preparations for women of reproductive age with iron deficiency anaemia in pregnancy (FRIDA): a systematic review and network meta-analysis. Lancet Haematol 2021; 8(7): e503-e512.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

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Created on September 21, 2022
Next planned update: 2025

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Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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