Your blood volume expands dramatically during pregnancy (up to 50%), and iron is essential for creating hemoglobin to carry oxygen to your tissues and your baby.
Recommended amount: 27 mg daily during pregnancy (up from 18 mg pre-pregnancy), if treating iron-deficiency anemia often an additional 60 mg of elemental iron is often prescribed.
While daily dosing of iron is most common, if iron is causing side effects such as constipation, metallic taste in the mouth, and stomach upset, it can be dosed every other day to reduce the GI side effects, particularly if your OB is recommending additional iron to treat iron-deficiency anemia on top of the 27 mg/day.
A 2015 study published in Blood found that every other day was equivalent to daily dosing in the treatment of iron depletion in young women. It seems that after taking an iron supplement your body isn’t able to absorb much until it has been >24-48 hrs from the initial dose. While this dosing regimen is well known to hematologists, it might not be to your ObGyn. However, this is well established in other fields of medicine and you can show your OB the first three sources listed for this article if they have questions. This would mean taking a different prenatal vitamin without iron (such as a gummy) on alternating days or taking a prenatal without iron every day and taking a separate iron supplement on the days it is needed such as Monday, Wednesday, and Friday.
Food sources: Lean red meat, poultry, fish, beans, lentils, fortified cereals
Different Forms
One of the most confusing aspects of iron supplementation is understanding “elemental iron” versus the total weight of an iron compound. This confusion can lead to taking too little or too much iron. When you see the RDA for iron during pregnancy (27 mg), this refers to the actual iron element itself, not the entire iron compound in your supplement. Different iron compounds contain different percentages of actual iron:
- Ferrous Sulfate: Commonly used, high elemental iron content (about 20% iron)
- Ferrous Gluconate: Lower elemental iron (about 12% iron), may cause less GI upset
- Ferrous Fumarate: High elemental iron (about 33% iron)
- Ferrous Bisglycinate (Iron Chelate): Better absorbed and may cause less digestive discomfort
If you need to meet the pregnancy RDA of 27 mg of elemental iron:
- You would need approximately 135 mg of ferrous sulfate
- You would need approximately 225 mg of ferrous gluconate
- You would need approximately 82 mg of ferrous fumarate
Common confusion with prescription iron:
Prescription iron supplements often list the compound amount prominently. For example, “Ferrous sulfate 325 mg” might only provide 65 mg of elemental iron. When your doctor recommends a specific amount of iron, always clarify whether they mean elemental iron or the total compound.
Key facts:
- Iron deficiency anemia is common in pregnancy and can cause fatigue and other complications
- Vitamin C helps your body absorb iron, so pair iron-rich foods with fruits and vegetables
- If constipation is an issue, talk to your healthcare provider about different iron formulations that may be gentler on your digestive system
Sources
Auerbach M., et al Treatment of iron deficiency and iron deficiency anemia in adults Uptodate Oct 08, 2025
Diego Moretti, et al, Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women,Blood, Volume 126, Issue 17, 2015, Pages 1981-1989, ISSN 0006-4971
Auerbach, Michael, and Stanley Schrier. “Treatment of iron deficiency is getting trendy.” The Lancet. Haematology vol. 4,11 (2017): e500-e501. doi:10.1016/S2352-3026(17)30194-1
Schrier, Stanley L. “So you know how to treat iron deficiency anemia.” Blood vol. 126,17 (2015): 1971. doi:10.1182/blood-2015-09-666511
Keats EC, Haider BA, Tam E, Bhutta ZA. Multiple-micronutrient supplementation for women during pregnancy. Cochrane Database Syst Rev 2019; 3.
Middleton P, Gomersall JC, Gould JF, et al. Omega-3 fatty acid addition during pregnancy. Cochrane Database Syst Rev 2018; 11.
Ramakrishnan U, Grant F, Goldenberg T, et al. Effect of women’s nutrition before and during early pregnancy on maternal and infant outcomes: a systematic review. Paediatr Perinat Epidemiol 2012; 26 Suppl 1:285.