Your body needs half again as much iron during pregnancy as before: 27 milligrams (mg) a day instead of 18. Most women can’t get that from food alone, which is why prenatal vitamins contain iron and why your blood gets checked for anemia.

The short version

  • How much: 27 mg a day during pregnancy, according to the NIH. Most prenatal vitamins contain about that amount.
  • The risks of low iron: Low iron in pregnancy raises the risk of anemia for you and of preterm birth and low birth weight for your baby. It may also affect your baby’s brain development.
  • How common it is: About 10% to 16% of pregnant women in the U.S. have iron deficiency, rising to about 25% in the third trimester.
  • More isn’t better: The upper limit is 45 mg a day from all sources, unless your provider prescribes more for a while to treat a deficiency.
  • Testing: The American College of Obstetricians and Gynecologists (ACOG) recommends checking for anemia in the first trimester and again at 24 to 28 weeks.

Why your iron needs go up

Iron is part of hemoglobin, the protein in red blood cells that carries oxygen. During pregnancy, the amount of blood in your body expands a great deal, and your baby and the placenta need iron to grow, according to the NIH. All of that takes iron.

Food usually doesn’t cover it. Pregnant women in the U.S. get about 17 mg of iron a day from food on average, and more than 8 in 10 fall short of the amount most women need, according to the NIH.

What low iron can do

Iron runs low in stages. First your stored iron drops. Then your body has trouble making red blood cells. Only at the last stage does it show up as iron-deficiency anemia on a blood test. So you can be low in iron before you’re anemic.

For you, anemia can mean tiredness, weakness, shortness of breath, trouble concentrating, and feeling cold. For your baby, iron deficiency during pregnancy is linked to preterm birth, low birth weight, low iron stores at birth, and effects on brain and behavioral development, according to the NIH.

Who is more likely to run low

  • Women in the third trimester, when needs peak
  • Vegetarians and vegans, because iron from plants is absorbed less well; the NIH says they need almost twice as much iron
  • Women with celiac disease, Crohn’s disease, ulcerative colitis, or past stomach or intestinal surgery
  • Women who had heavy periods or low iron before pregnancy
  • Frequent blood donors

Too much iron is a problem too

Extra iron isn’t automatically safer.

  • The upper limit is 45 mg a day from food, drinks, and supplements combined. About 28% of pregnant women in the U.S. go over it once supplements are counted, according to the NIH.
  • Side effects: Doses of 45 mg a day or more can cause nausea and constipation.
  • Possible risks when you aren’t low: In women who already have enough iron, some studies have linked extra iron or high iron levels to gestational diabetes, preterm birth, and slower fetal growth. The NIH describes the risk as U-shaped: problems with too little and with too much.
  • Hemochromatosis: People with this inherited condition absorb too much iron and should avoid iron supplements unless their doctor says otherwise.

If you’re diagnosed with iron deficiency, your provider may prescribe more than 45 mg for a while to rebuild your stores. That’s a treatment for a deficiency. It doesn’t mean everyone should take more.

What the guidelines say

Expert groups agree that iron matters in pregnancy. They differ on whether every pregnant woman should take extra iron, because of that U-shaped risk. This summary comes from the NIH.

Organization What it recommends
ACOG Low-dose iron for all pregnant women, starting in the first trimester. Check for anemia in the first trimester and again at 24 to 28 weeks. Extra iron, on top of a prenatal vitamin, for women with iron-deficiency anemia.
U.S. Preventive Services Task Force The evidence isn’t strong enough to recommend for or against routine iron testing or routine iron supplements for pregnant women without symptoms.
Dietary Guidelines for Americans Take an iron-containing supplement when your obstetrician or other provider recommends it.
World Health Organization 30 to 60 mg of iron plus 400 mcg of folic acid a day, with the higher dose where anemia is common.

In practice, most U.S. women get iron through a prenatal vitamin, which typically has about 27 mg, and get tested for anemia during pregnancy. If your results show you’re low, your provider will recommend more.

How to get enough

  1. Take your prenatal vitamin every day. Check that it lists about 27 mg of iron; many gummy prenatals have none. See Prenatal Vitamin Questions, Answered.
  2. Eat iron-rich foods and help your body absorb them. Pair plant sources of iron with vitamin C foods, and take calcium supplements at a different time of day. See Iron-Rich Foods for Pregnancy.
  3. Get tested. Ask about your results at your first-trimester visit and at 24 to 28 weeks. See Iron Levels in Pregnancy: Tests and What Your Results Mean.
  4. If you’re low, take the iron your provider prescribes, and ask for help if it upsets your stomach. See Iron Supplements in Pregnancy.

Related reading: Folic Acid and Anemia explains how iron, folate, and B12 anemia differ. Craving ice can be a sign of low iron. And iron matters for your baby after birth too: see Delayed Cord Clamping and Iron for Breastfed Babies.

What to do now

  • Check your prenatal vitamin label for about 27 mg of iron.
  • Add up iron from any other supplements so you stay under 45 mg unless your provider says otherwise.
  • Ask your provider for your anemia test results at your next visit.
  • If you’re vegetarian or vegan, ask whether you need extra iron.

Related reading

Sources

Updated October 2026. This article is for general information and is not a substitute for advice from your health care provider.