Iron Deficiency During Pregnancy

Iron deficiency is one of the most important nutritional problems to look for during pregnancy, because pregnancy substantially increases the amount of iron your body needs. It is also something that is usually very treatable when identified early. One important distinction first:

  • Iron deficiency = your body's iron stores are becoming depleted.
  • Iron-deficiency anaemia (IDA) = iron deficiency has progressed far enough that haemoglobin/red-blood-cell production is affected and your haemoglobin is low. You can therefore be iron deficient before you become anaemic. That is one reason checking ferritin—not just haemoglobin—can be useful. 1. Why pregnancy puts you at risk of iron deficiency Your iron requirements increase substantially during pregnancy because iron is needed for:
  • making additional maternal red blood cells
  • increasing your blood volume
  • the placenta
  • the developing baby's blood and tissues
  • building the baby's iron stores for the first months after birth
  • compensating for blood loss during delivery WHO estimates that 37% of pregnant women globally have anaemia, and at least a substantial proportion is attributable to iron deficiency. This is why iron isn't just a "vitamin" issue during pregnancy. Iron is fundamental to oxygen delivery.

2. What iron actually does Iron is a component of haemoglobin. Haemoglobin is the protein inside red blood cells that carries oxygen from your lungs to your:

  • brain
  • heart
  • muscles
  • placenta
  • baby Think of it as: Iron → haemoglobin → oxygen transport If iron becomes severely depleted, your body cannot produce enough healthy haemoglobin. The result is anaemia. Your heart may then have to work harder to deliver enough oxygen around the body.

3. Why iron deficiency can be particularly important during pregnancy Iron deficiency/anaemia can affect both mother and baby. Maternal effects can include:

  • significant fatigue
  • weakness
  • dizziness/light-headedness
  • headaches
  • shortness of breath
  • reduced exercise tolerance
  • palpitations/rapid heartbeat
  • difficulty concentrating
  • feeling cold
  • reduced ability to cope with blood loss at delivery WHO notes that anaemia in pregnancy is associated with adverse maternal and birth outcomes, including premature birth, low birth weight and maternal morbidity/mortality. There is also concern about the baby's iron supply and neurodevelopment when significant maternal iron deficiency is untreated. The evidence is strongest for significant iron deficiency/anaemia rather than mild isolated reductions in iron stores.

4. Why you shouldn't wait until you feel tired This is important. Fatigue is extremely common in pregnancy even when iron is normal. And you can have depleted iron stores before you develop obvious anaemia. So: Feeling okay doesn't necessarily mean your iron is okay. Conversely, feeling exhausted doesn't automatically mean you are iron deficient. That's why blood testing is much more useful than symptoms alone.

5. What blood tests should be checked? A useful iron/anaemia assessment generally starts with a full blood count (FBC/CBC) and, where appropriate, iron studies. The main tests are:

  • Haemoglobin (Hb) — whether you are anaemic
  • Haematocrit (Hct) — percentage of blood made up of red cells
  • MCV — average size of red blood cells
  • MCH/MCHC — haemoglobin content of red cells
  • Ferritin — your stored iron
  • Transferrin/TIBC — iron-binding capacity
  • Transferrin saturation (TSAT) — how much transferrin is carrying iron
  • Serum iron — iron circulating in blood

Of these, ferritin is particularly useful for identifying depleted iron stores. A 2025 obstetric haematology consensus recommends defining iron deficiency in pregnancy as ferritin <30 µg/L (ng/mL) and recommends ferritin testing at booking and around 24–28 weeks. However, different countries and organisations use somewhat different testing strategies, so your doctor may not order every test.

6. What does haemoglobin actually mean? Pregnancy naturally changes your blood. Your plasma volume increases substantially, so your blood becomes somewhat diluted. Consequently, haemoglobin thresholds for anaemia are lower during pregnancy. WHO uses approximately:

  • 1st trimester: Hb <110 g/L (11 g/dL)
  • 2nd trimester: Hb <105 g/L (10.5 g/dL)
  • 3rd trimester: Hb <110 g/L (11 g/dL) for diagnosing anaemia. So a haemoglobin of 10.5 g/dL means something different depending on which trimester you're in and what the rest of your blood results show.

7. Ferritin is extremely important Imagine your body has an iron "bank account." Ferritin tells you roughly how much is in the bank. You can have: Normal haemoglobin + low ferritin which means: "I'm not anaemic yet, but my iron reserves are running low." Eventually: Low ferritin + low haemoglobin can become: iron-deficiency anaemia. This distinction matters because treating depleted iron stores earlier may prevent progression to significant anaemia later in pregnancy. One complication Ferritin is also an acute-phase reactant. That means inflammation or infection can make ferritin look higher than your true iron stores. So a "normal" ferritin doesn't always completely exclude iron deficiency if there is significant inflammation.

8. What causes iron deficiency during pregnancy? There are several possibilities. Before pregnancy You may already have entered pregnancy with low iron stores because of:

  • heavy periods
  • low dietary iron
  • vegetarian/vegan diet without adequate iron planning
  • previous pregnancy
  • closely spaced pregnancies
  • previous blood loss
  • previous iron deficiency
  • gastrointestinal absorption problems During pregnancy Iron requirements increase. You may therefore become deficient even if your diet was previously adequate. Other causes can include:
  • inadequate iron supplementation
  • poor absorption
  • severe nausea/vomiting
  • gastrointestinal disease
  • previous bariatric surgery
  • chronic inflammation
  • bleeding Your doctor may investigate the underlying cause rather than simply giving you iron indefinitely.

9. How much iron do you actually need? There are two different concepts: Preventing deficiency WHO recommends routine pregnancy supplementation with: 30–60 mg elemental iron + 400 µg folic acid daily for prevention of maternal anaemia and certain adverse outcomes. Treating established iron deficiency/anaemia This generally requires more iron than is contained in an ordinary prenatal vitamin, depending on the severity and your clinician's treatment plan. This is an important distinction. A prenatal vitamin containing a relatively small amount of iron may be adequate for prevention, but may not be enough to correct established iron-deficiency anaemia.

10. Food can help — but food alone may not correct significant deficiency Iron-rich foods include: Heme iron — absorbed relatively well

  • red meat
  • liver (but liver is generally avoided/restricted during pregnancy because of its high vitamin A content)
  • poultry
  • fish and seafood Non-heme iron
  • lentils
  • beans
  • chickpeas
  • tofu
  • spinach and other leafy greens
  • iron-fortified cereals
  • nuts and seeds Vitamin C helps Vitamin C improves absorption of non-heme iron. For example: lentils + tomatoes/peppers or iron-fortified cereal + fruit can improve iron absorption. WHO also recommends eating vitamin-C-rich foods alongside iron-rich foods.

11. Things that interfere with iron absorption This is one of the most useful practical points. Iron absorption can be reduced when iron is taken with:

  • tea
  • coffee
  • calcium
  • some dairy products
  • high-phytate foods WHO specifically recommends avoiding tea, coffee, cocoa and calcium around iron-rich meals/supplements because they can reduce absorption. Example If you take your iron tablet with: coffee + milk you may absorb considerably less iron than if you take it separately. A common practical approach is to take iron away from calcium and tea/coffee, provided your clinician/pharmacist agrees with the schedule.

12. Oral iron — the usual first treatment For established iron deficiency or iron-deficiency anaemia, oral iron is usually the first-line treatment. One of the most commonly used forms is: ferrous sulfate Other formulations include:

  • ferrous fumarate
  • ferrous gluconate
  • other iron preparations The important number on the label is elemental iron, not simply the total weight of the iron compound. For example, a tablet saying "ferrous sulfate 325 mg" does not mean 325 mg of elemental iron. This is why you shouldn't compare products solely by the large number printed on the front.

13. The biggest problem with oral iron: side effects Iron tablets commonly cause:

  • constipation
  • nausea
  • stomach pain
  • bloating
  • diarrhoea in some people
  • metallic taste
  • dark/black stools GI side effects can be significant enough that people stop taking their medication. One review notes that gastrointestinal problems occur frequently with oral iron and can substantially reduce adherence. So if iron makes you feel awful: don't simply stop and suffer. Tell your doctor. There are different formulations and dosing approaches.

14. Does taking iron every other day work? There is growing evidence that alternate-day oral iron can improve tolerability and iron absorption in some circumstances. A 2025 obstetric haematology consensus says alternate-day dosing can be considered to reduce side effects, although evidence and recommendations differ between guidelines and particularly for established anaemia. So don't automatically assume: "More tablets = more iron absorbed." Iron absorption is biologically complicated, partly because of a hormone called hepcidin, which regulates iron absorption. Your doctor can decide whether daily or alternate-day treatment is appropriate.

15. What if oral iron doesn't work? This is where intravenous (IV) iron becomes important. IV iron is delivered directly into a vein.

  • How it enters the body: oral goes through your digestive system; IV goes directly into the bloodstream
  • Cost: oral is usually cheaper; IV is more expensive
  • Speed: oral works gradually; IV works faster
  • GI side effects: common with oral; much less with IV
  • Infusion reaction: not applicable to oral; possible with IV
  • First trimester: oral is generally used; IV is usually avoided because safety data are limited
  • Later pregnancy: oral is common; IV is useful when needed
  • Severe deficiency: oral may be insufficient/too slow; IV is often considered
  • Poor absorption: oral may not work well; IV bypasses the gut
  • Need for a medical visit: usually not for oral; yes for IV

Instead of relying on your digestive system to absorb the iron: IV → bloodstream → iron available for use/storage It can replenish iron much faster.

16. When might IV iron be considered? ACOG considers IV iron for people who:

  • cannot tolerate oral iron
  • don't respond adequately to oral iron
  • have severe iron deficiency later in pregnancy The American Society of Haematology notes that IV iron is generally used in the second or third trimester, because safety data in the first trimester are limited. It may be especially useful when:
  • haemoglobin is significantly low
  • pregnancy is already advanced
  • delivery is approaching
  • oral iron hasn't worked
  • oral iron causes intolerable GI symptoms
  • absorption is poor
  • rapid correction is desirable

17. Is IV iron safe during pregnancy? Modern IV iron preparations are generally considered safe when appropriately used, particularly in the second and third trimesters. Recent evidence suggests IV iron can raise haemoglobin somewhat faster than oral iron, with serious adverse reactions uncommon. But it isn't completely risk-free. Potential problems include:

  • infusion reactions
  • headache
  • nausea
  • dizziness
  • flushing
  • low blood pressure
  • rarely, serious allergic reactions Some preparations can also cause hypophosphataemia (low phosphate), which is one reason the choice of IV preparation matters.

18. What happens during an iron infusion? Usually:

  • A nurse places an IV cannula.
  • Iron medication is diluted/prepared.
  • It is administered through the IV.
  • You are monitored during and after the infusion.
  • Your blood results are rechecked later to see how you've responded. Some modern formulations can deliver a large replacement dose in one or a small number of visits, while others require multiple infusions.

19. Oral iron vs IV iron Both are legitimate treatments. IV isn't automatically "better." It's particularly valuable when oral treatment isn't working, isn't tolerated, or there's not enough time to correct the deficiency before delivery.

20. What happens if you don't treat it? This is why screening matters. Untreated significant iron-deficiency anaemia can leave you entering labour with inadequate haemoglobin. That's particularly important because delivery involves blood loss. If you already have significant anaemia before delivery, you have less reserve if substantial bleeding occurs. Anaemia during pregnancy is associated with increased risks of adverse maternal and fetal outcomes, including premature birth and low birth weight. There are also concerns about maternal fatigue, reduced physical capacity and fetal/newborn iron status.

21. Iron deficiency isn't the only cause of anaemia This is extremely important. If your haemoglobin is low, don't automatically assume you need enormous amounts of iron. Other causes include:

  • folate deficiency
  • vitamin B12 deficiency
  • blood loss
  • chronic inflammation
  • kidney disease
  • infections
  • inherited conditions such as thalassaemia
  • sickle-cell disorders
  • other haemoglobin disorders WHO specifically notes that anaemia has multiple causes and that iron deficiency is only one of them. This is especially important in populations where inherited haemoglobin disorders are relatively common.

22. Thalassaemia is an important example Someone with thalassaemia trait can have:

  • low MCV
  • small red blood cells
  • mild anaemia and appear superficially similar to iron deficiency. But giving large amounts of iron when iron stores are actually normal isn't the solution. This is why doctors sometimes look at: Hb + MCV + ferritin + other tests rather than treating every low haemoglobin as iron deficiency.

23. What should you ideally check during pregnancy? A sensible conversation with your obstetrician/midwife would include: At the beginning of pregnancy FBC/CBC plus consideration of: Ferritin particularly if you have a history of:

  • anaemia
  • heavy periods
  • previous iron deficiency
  • previous pregnancy
  • vegetarian/vegan diet
  • multiple pregnancy
  • closely spaced pregnancies
  • previous postpartum haemorrhage
  • gastrointestinal problems Some newer obstetric haematology guidance recommends ferritin routinely at booking and again around 24–28 weeks. Around 24–28 weeks Repeat: FBC and, depending on your care pathway: ferritin/iron studies Later pregnancy Testing may be repeated if:
  • you were previously deficient
  • haemoglobin is falling
  • symptoms develop
  • treatment isn't working
  • delivery is approaching and anaemia remains significant

24. How do you know treatment is working? Your doctor doesn't simply give you iron and forget about it. Blood tests can be repeated to see whether:

  • haemoglobin is rising
  • ferritin is improving
  • red-cell indices are normalising
  • symptoms are improving If haemoglobin doesn't respond as expected, you need to ask why. Possibilities include:
  • you're not absorbing the iron
  • you're not taking enough
  • side effects are preventing adherence
  • ongoing blood loss
  • inflammation
  • B12/folate deficiency
  • thalassaemia/another haemoglobin disorder
  • incorrect diagnosis That's a reason to reassess rather than simply taking increasingly large amounts of iron.

25. Can you take too much iron? Yes. Iron is essential, but more is not automatically better. Excessive iron can cause:

  • nausea
  • abdominal pain
  • constipation
  • vomiting
  • toxicity in overdose
  • potentially dangerous iron accumulation in particular medical conditions So don't take multiple iron-containing products on top of one another without checking the elemental iron dose. For example, you might unknowingly take: prenatal vitamin + separate iron tablet + another multivitamin containing iron and substantially increase your total intake.

26. What I would consider the "ideal" approach If you're planning pregnancy or are pregnant, the goal isn't: "Wait until haemoglobin becomes very low." A better approach is: Before/early pregnancy ↓ Check FBC + iron status/ferritin when appropriate ↓ Identify depleted iron stores early ↓ Correct the deficiency ↓ Recheck blood results ↓ Continue appropriate pregnancy supplementation ↓ Reassess later in pregnancy ↓ Make sure haemoglobin/iron status is adequate going into delivery This is particularly important because iron requirements continue throughout pregnancy.

27. A very practical example Imagine someone has: Hb = 12.0 g/dL Ferritin = 12 ng/mL Their haemoglobin is technically okay. But their iron stores are depleted. That's different from: Hb = 9.0 g/dL Ferritin = 5 ng/mL The second person has significant iron-deficiency anaemia and needs substantially more urgent treatment. And that's different again from: Hb = 9.0 g/dL Ferritin = 80 ng/mL That person is anaemic, but iron deficiency may not be the explanation. The numbers have to be interpreted together.

28. The most important tests to ask about If you're pregnant, I would ask your doctor: "What is my haemoglobin and what is my ferritin?" And, if abnormal: "Is this iron deficiency, iron-deficiency anaemia, or another type of anaemia?" Then: "How much elemental iron am I getting from my prenatal vitamin?" And if you are deficient: "Do I need therapeutic-dose oral iron, and when should we repeat my blood tests?" If oral iron isn't tolerated: "Would IV iron be appropriate for me, considering how far along I am?" Those questions are much more useful than simply asking whether you should "take an iron supplement."

The bottom line Iron deficiency during pregnancy is common, important and treatable. The progression can look like: Low iron stores ↓ Iron deficiency ↓ Low haemoglobin / iron-deficiency anaemia ↓ Reduced oxygen-carrying capacity ↓ Greater maternal and pregnancy risks The best way to catch it is through blood testing rather than symptoms alone. For prevention, WHO recommends 30–60 mg elemental iron + 400 µg folic acid daily during pregnancy. For established deficiency, treatment is individualized. Oral iron is generally first-line, while IV iron becomes an important option when oral iron isn't tolerated, doesn't work, the deficiency is severe, or there isn't enough time to correct it before delivery. And perhaps the most important point: Don't look at haemoglobin alone. Ferritin tells you much more about whether your iron reserves are actually being depleted.