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Is iron safe during pregnancy?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

NIH gives 27 mg of iron a day in pregnancy and an upper limit of 45 mg. A Cochrane review of 57 trials in 48,971 women called the evidence on adverse effects very uncertain, with 21.6% reporting them on iron against 18.0% without. NIH notes that professional groups disagree on routine iron in pregnancy.1,2

Key facts

  • NIH gives 27 mg of iron a day in pregnancy for teens and women, against 18 mg for women 19 to 50 who are not pregnant.1,3
  • The upper limit is 45 mg a day from food and supplements, set from stomach and bowel effects, and doctors sometimes prescribe more.1,3
  • NIH says about 72% of pregnant women in the US use a supplement that contains iron.1
  • The Cochrane review called the evidence on adverse effects very uncertain, at 21.6% on iron against 18.0% on placebo or no iron.2
  • NIH says ACOG recommends low-dose iron from the first trimester, while the U.S. Preventive Services Task Force found the evidence insufficient to judge benefits and harms in women without symptoms.1

What NIH says about iron in pregnancy

NIH says the amount of iron needed rises in pregnancy because the blood volume and red cell mass expand. It reports that iron deficiency during pregnancy increases the risk of premature birth and low birth weight, and that the Dietary Guidelines for Americans advise pregnant women to take an iron supplement when recommended by an obstetrician or other health care provider.1

Pregnant women need 27 mg of iron a day. Breastfeeding women need 9 mg, or 10 mg if they are 18 or younger.1,3

The upper limit for iron from food and supplements is 45 mg a day for anyone 14 or older and 40 mg for younger children. It was set to avoid stomach and bowel side effects, and doctors sometimes prescribe more for a while to rebuild low stores.1,3

About 14% to 18% of Americans use a supplement that contains iron, from 6% of children aged 12 to 19 to 72% of pregnant women.1

Do experts agree on iron supplements in pregnancy?

No, according to NIH. The American College of Obstetricians and Gynecologists recommends low-dose iron starting in the first trimester and screening for anemia, while the U.S. Preventive Services Task Force concluded that the current evidence is insufficient to assess the balance of benefits and harms of routine iron supplementation in pregnant women without symptoms. The Task Force statement does not apply to women who are severely malnourished, have symptoms of iron deficiency or have conditions that raise iron needs.1

That disagreement is a reason the question belongs with an obstetrician or midwife, who can check blood tests before any supplement is started.1

What did the Cochrane review find about harms?

The review pooled 57 trials with 48,971 women. For daily oral iron against placebo or no iron, it found the evidence on adverse effects very uncertain: 21.6% of women reported adverse effects on iron against 18.0% without, with a risk ratio of 1.29 (0.83 to 2.02) in 12 trials. For iron with folic acid it found low-certainty evidence of more adverse effects in one trial of 456 women, so the range was very wide.2

The review's main outcomes were anemia and birth outcomes, and it found probably little or no difference in maternal death, preterm birth or congenital anomalies. A separate meta-analysis of eight trials in 2,822 pregnant women who had normal iron status looked at the same kind of outcomes, and its abstract does not list side effects.2,4

What side effects and cautions apply?

The documented side effects are those of iron in general: high doses, especially on an empty stomach, can cause upset stomach, constipation, nausea, abdominal pain, vomiting and diarrhea. NIH adds that supplements with 25 mg of iron or more can reduce zinc absorption.1,3

High doses of iron supplements, especially on an empty stomach, can cause upset stomach, constipation, nausea, abdominal pain, vomiting and diarrhea. Doses of 45 mg a day or more are the most likely to cause them.1,3

Supplements with 25 mg of iron or more can reduce zinc absorption and blood zinc levels.1

People with hereditary hemochromatosis absorb too much iron, and NIH advises them to avoid iron and vitamin C supplements. Iron tablets are also a leading cause of fatal poisoning in children under 6, which is why the label warns to keep iron out of a child's reach.1,3

What about iron infusions, transfusions and bisglycinate?

The sources on this page cover iron taken by mouth. They do not address iron infusions given through a vein or blood transfusions in pregnancy, which a doctor manages and which is not a finding either way.1

Ferrous bisglycinate is iron bound to the amino acid glycine. NIH says forms of iron such as iron amino-acid chelates, carbonyl iron and heme iron polypeptides might have fewer gastrointestinal side effects than ferrous or ferric salts. It does not describe bisglycinate in pregnancy specifically, and the same upper limit applies.1

Who should ask a doctor about iron in pregnancy

  • Anyone pregnant who is thinking about starting iron, who should ask their doctor or midwife about a blood test first, since NIH says hemoglobin tests are neither sensitive nor specific for iron deficiency and are often combined with ferritin.1
  • Anyone pregnant who takes levothyroxine, levodopa, an antibiotic, dolutegravir or a medicine that lowers stomach acid.1
  • Anyone pregnant with hemochromatosis or another iron overload condition.1
  • Anyone pregnant who also takes a multivitamin and a separate iron product, who should ask a pharmacist to add them up against the 45 mg upper limit.1,3

Questions people ask

Is an iron supplement safe during pregnancy?

NIH gives 27 mg a day in pregnancy and an upper limit of 45 mg. A Cochrane review called the evidence on adverse effects very uncertain. Ask your doctor or midwife whether iron fits you.1,2

Is iron infusion safe during pregnancy?

The sources checked cover iron taken by mouth, not infusions, which is not a finding either way. Ask your doctor, who decides when an infusion is needed.1

Is iron transfusion safe during pregnancy?

A transfusion is not an iron supplement, and the sources checked do not address it. Ask your doctor.1

Is iron bisglycinate safe during pregnancy?

NIH says iron amino-acid chelates might have fewer stomach and bowel side effects than ferrous or ferric salts, and the 45 mg upper limit still applies. Ask your doctor or pharmacist.1

Is taking iron safe in early pregnancy?

NIH gives one pregnancy amount, 27 mg a day, and says ACOG recommends low-dose iron from the first trimester. Ask your doctor or midwife about your own blood tests.1

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Sources

  1. Office of Dietary Supplements, National Institutes of Health. Iron: Fact Sheet for Health Professionals. Updated September 4, 2025. Opened 2026-10-07.
  2. Finkelstein JL, Cuthbert A, Weeks J, Venkatramanan S, Larvie DY, De-Regil LM, et al. Daily oral iron supplementation during pregnancy. Cochrane Database Syst Rev. 2024;8:CD004736. A Cochrane systematic review of randomized trials. Opened 2026-10-11.
  3. Office of Dietary Supplements, National Institutes of Health. Iron: Fact Sheet for Consumers. Updated August 17, 2023. Opened 2026-10-07.
  4. Hansen R, Sejer EPF, Holm C, Schroll JB. Iron supplements in pregnant women with normal iron status: A systematic review and meta-analysis. Acta Obstet Gynecol Scand. 2023;102(9):1147-1158. A systematic review and meta-analysis of randomized trials. Opened 2026-10-11.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.