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Pregnancy and birth: Do all pregnant women need to take iron supplements?

Last Update: March 19, 2014; Next update: 2017.

Iron supplements are particularly important for pregnant women who have anemia. In women who have normal blood values, taking iron supplements as a precautionary measure probably does not have any health benefits. They can 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 is not 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. 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 someone’s hemoglobin levels are lower than this, the iron levels in their blood are measured too. This can help determine whether their low hemoglobin levels are due to a lack of iron (iron deficiency). Because the body can store a certain amount of iron, another blood value is also measured to find out how full the body’s iron stores are. If someone’s iron stores are empty but their hemoglobin levels are normal, they are said to have latent (hidden) or non-anemic iron deficiency.

Women have several blood tests during pregnancy. One thing that is tested is their iron levels, so iron deficiency anemia can be detected early on and treated using iron supplements.

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 absorb iron from plant-based foods. But some plants are also good sources of iron. 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.

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

What are the consequences of iron deficiency in pregnancy?

Iron deficiency anemia can make you feel tired and exhausted. Severe anemia can also lead to complications in pregnancy. For instance, it can weaken the mother’s immune system and make infections more likely. It also increases the risk of the baby weighing too little at birth (low birth weight).

Severe anemia is rare in healthy pregnant women who eat a balanced diet. But anemia can cause serious health problems in women who do not, or cannot, eat a balanced diet.

When does it make sense to take iron supplements?

A lot of pregnant women take iron supplements because they think their bodies need more iron during pregnancy. Pregnant women with normal blood values are also often advised to take iron supplements in order to prevent anemia. Mild anemia does not affect the child, though.

Anemia is only a problem if it is more severe and lasts a long time. If someone is diagnosed with iron deficiency anemia, they will usually be prescribed high-dose iron supplements.

According to German health authorities, pregnant or breastfeeding women need 20 to 30 mg of iron per day. It can be particularly difficult for vegetarians to get that amount of iron in their diet alone. But iron deficiency problems would be detected in the standard blood tests.

Do women with normal blood values benefit from taking iron supplements?

There are more than 60 studies on the use of iron supplements in pregnancy. A total of more than 30,000 women took part in the studies. The results show that, if women have normal blood values, taking 30 mg of iron per day as a precautionary measure does not have any noticeable health benefits for them or for their children. Although iron supplements were found to lower the risk of anemia, they did not influence the number of preterm births or infections in pregnant women.

Advantages and disadvantages depend on the dose

The results were slightly different in studies where women took 60 mg of iron per day. Their children were less likely to be born with a low birth weight (below 2,500 grams):

  • Without iron supplements: If mothers took a fake drug (placebo) instead of iron, about 5 out of 100 children were born with a low birth weight.
  • With iron supplements: If mothers took 60 mg of iron per day, about 4 out of 100 children were born with a low birth weight.

In other words: Taking high-dose iron supplements prevented low birth weight in 1 out of 100 children. One of the studies also found that women who took high-dose iron supplements were somewhat less likely to need a blood transfusion.

But higher amounts of iron were also clearly associated with a higher risk of side effects.

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 side effects. These include, in particular, 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. In the studies, gastrointestinal problems occurred in

  • about 3 out of 100 women who only took a placebo drug, compared to
  • about 23 out of 100 women who took 60 mg of iron per day.

In other words: When taken at a dose of 60 mg per day, iron supplements caused side effects in about 20 out of 100 women.

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 even 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 lower the likelihood of side effects. But it is not clear whether that is really the case.

Keep iron supplements out of children’s reach

Like all medications, iron tablets should be kept out of children’s reach. Even if iron is “only” a natural mineral, an accidental overdose can be life-threatening for children.

Sources

  • Haider BA, Olofin IO, Wang M, Spiegelman D, Ezzati M, Fawzi WW. Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis. BMJ 2013; 346: f3443. [PMC free article: PMC3689887] [PubMed: 23794316]
  • Pena-Rosas JP, Viteri FE. Daily oral iron supplementation during pregnancy. Cochrane Database Sys Rev 2012; (12): CD004736. [PMC free article: PMC4233117] [PubMed: 23235616]
  • Peña-Rosas JP, De-Regil LM, Dowswell T, Viteri FE. Intermittent oral iron supplementation during pregnancy. Cochrane Database Sys Rev 2012; (7): CD009997.
  • 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. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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