Iron deficiency and anaemia in pregnancy: understanding blood tests, food and supplements

Iron comes up frequently in pregnancy: fatigue, blood tests, ferritin, haemoglobin, supplements, constipation and plenty of conflicting information. Significant tiredness does not automatically mean iron deficiency. Iron deficiency is also not exactly the same as anaemia. Conversely, automatically attributing marked fatigue to pregnancy can mean overlooking an abnormality that deserves assessment.

This guide explains the key concepts, tests, role of diet and role of treatment. It draws on recent French guidance from the Haute Autorité de santé (HAS), together with WHO, ANSES, French National Health Insurance, NIH, FIGO and Cochrane sources. It does not replace antenatal care: interpretation of blood tests and decisions about supplementation depend on gestational stage, laboratory results, symptoms, medical history and individual circumstances.

Why do iron requirements increase during pregnancy?

Iron is essential for haemoglobin, the protein in red blood cells that carries oxygen. During pregnancy, the maternal body has to meet several demands at once: expansion of blood volume, placental development and the developing baby's needs. French National Health Insurance notes that requirements increase with fetal and placental growth and expansion of maternal blood volume. See the French National Health Insurance overview of iron deficiency.

ANSES also identifies iron intake as an important nutritional consideration during pregnancy. This does not mean every pregnant woman becomes deficient or needs the same supplement dose. Starting iron stores, dietary pattern, closely spaced or multiple pregnancies, gastrointestinal conditions and other factors all affect individual risk.

This distinction matters because guidelines can have different purposes. A global public-health recommendation may aim to reduce anaemia across whole populations, whereas French clinical guidance can specify how deficiency should be investigated and treated in an individual receiving antenatal care.

Iron deficiency and anaemia are not the same thing

Iron deficiency means iron stores are insufficient. Anaemia means haemoglobin is below the threshold used for the relevant clinical context. Iron deficiency can therefore exist before haemoglobin falls far enough to meet the definition of anaemia. French National Health Insurance explicitly notes that persistent iron deficiency precedes iron-deficiency anaemia.

Conversely, not every anaemia is caused by iron deficiency. Vitamin B12 or folate deficiency, inflammatory disease, haemoglobin disorders, blood loss and other conditions can be involved. Taking iron simply because haemoglobin is low is therefore not a complete diagnostic approach.

Which thresholds does French HAS guidance use in obstetrics?

The HAS practical sheet on diagnosis and treatment of anaemia and iron deficiency in obstetrics defines anaemia as haemoglobin below 11 g/dL and iron deficiency as ferritin below 30 µg/L. It then distinguishes degrees of anaemia and proposes management accordingly. These are thresholds from this French obstetric guideline and should not be mixed indiscriminately with values from other populations or guidelines. See the HAS obstetric guidance.

You may encounter different thresholds elsewhere. Some general or international guidelines use different definitions depending on trimester and purpose. That does not necessarily mean one source is wrong: population, setting and clinical purpose matter. In a pregnancy managed in France, results should be interpreted by the clinician who knows the pregnancy and the laboratory context.

What do haemoglobin and ferritin tell us?

Haemoglobin

Haemoglobin is the oxygen-carrying protein in red blood cells and its measurement is central to diagnosing anaemia. Plasma volume expands substantially in pregnancy, changing measured blood concentrations. This physiological adaptation is one reason results need an obstetric interpretation rather than a threshold selected out of context.

HAS recommends screening for anaemia with a full blood count early in pregnancy, at the sixth month and whenever suggestive symptoms occur. This is a French screening recommendation; additional tests may still be appropriate in individual circumstances.

Ferritin

Ferritin is used as a marker of iron stores. A low ferritin strongly supports iron deficiency. HAS recommends ferritin testing when anaemia symptoms are present and, from early pregnancy, in some people with risk factors.

Ferritin is also influenced by inflammation. A normal or high result can therefore be harder to interpret in an inflammatory context. HAS reiterated in 2026 that inflammation affects ferritin interpretation, another reason not to interpret one number in isolation.

Why is serum iron alone not enough?

Circulating iron varies and does not, on its own, provide a simple measure of body iron stores. Depending on the situation, clinicians may consider the blood count, ferritin and sometimes other markers such as transferrin or transferrin saturation. The appropriate panel depends on the clinical question.

Who is at greater risk of iron deficiency?

HAS lists situations in which looking for deficiency may be particularly relevant, including high parity, multiple or closely spaced pregnancies, socioeconomic vulnerability, inflammatory bowel disease or gastrointestinal resection, dietary deficiencies and eating patterns that provide little iron or contain substances that reduce absorption. Vegetarian or vegan diets may also deserve particular nutritional attention without automatically implying deficiency.

Low stores before conception can make it harder to meet increased pregnancy requirements. Assessment therefore does not begin only in the third trimester: previous menstrual blood loss, pregnancy history, diet and medical history can all matter.

Which symptoms can occur with anaemia?

Fatigue, pallor, breathlessness on exertion, headaches, dizziness, weakness, palpitations and difficulty concentrating can occur with anaemia. French National Health Insurance also mentions restless legs among possible manifestations of iron deficiency or iron-deficiency anaemia. See the French guidance on symptoms and diagnosis.

None of these symptoms is specific. Fatigue and some exertional breathlessness can also occur in an uncomplicated pregnancy. Symptoms alone can neither confirm nor exclude iron deficiency; blood testing is much more informative than an online symptom checklist.

If tiredness is affecting daily life, our guide on pregnancy, work and fatigue discusses practical organisation and reasons to seek professional advice without assuming iron is the cause.

What can diet contribute?

A varied diet contributes iron and remains important even when treatment is needed. Haem iron is found in animal foods, while non-haem iron occurs in foods including pulses, grains, seeds, nuts and some vegetables. Their bioavailability differs.

The NIH notes that lean meat, seafood and poultry provide haem and non-haem iron, while beans, lentils, spinach, peas, nuts and some fortified grain products provide non-haem iron. US dietary references use 27 mg/day during pregnancy, but this is a US nutritional reference intake, not a prescription for an iron supplement. See the NIH professional iron fact sheet.

Examples of food sources

Depending on dietary pattern, iron can come from thoroughly cooked meat, pregnancy-appropriate fish, eggs, lentils, chickpeas, beans, tofu, fortified cereals, green vegetables, seeds and nuts. Pregnancy food-safety rules remain the priority: increasing iron intake never justifies eating foods that are unsafe or insufficiently cooked during pregnancy.

French National Health Insurance recommends a balanced, varied diet and identifies pulses, fish and meat as iron sources. See French pregnancy nutrition guidance.

Vitamin C and plant iron

Vitamin C improves absorption of non-haem iron. Pairing lentils with vitamin-C-rich vegetables or adding suitable fruit to a plant-based meal is a simple dietary strategy. It can support intake but should not be presented as sufficient treatment for established anaemia.

Tea, coffee and absorption

Polyphenols in tea and coffee can reduce absorption of non-haem iron when consumed at the same time. There is no need to turn every meal into a timed protocol. If iron status is a concern or treatment has been prescribed, ask how to organise doses while also respecting pregnancy guidance on caffeine.

Why does food not always correct deficiency?

When stores are very low or iron-deficiency anaemia is established, increasing iron-rich foods may not correct the problem quickly enough. It is important to distinguish nutritional prevention from treatment of diagnosed deficiency. The first supports adequate intake; the second uses therapeutic doses according to a diagnosis.

This avoids two opposite mistakes: believing a perfect diet guarantees that deficiency cannot occur, or assuming prescribed iron makes diet irrelevant. The approaches can complement each other but have different purposes.

Should you take iron 'just in case'?

Self-medication is not the preferred approach in France. HAS defines screening and treatment situations, and French National Health Insurance notes that a doctor or midwife may prescribe iron when needed. Supplementation should therefore sit within antenatal care.

WHO takes a global public-health perspective and recommends daily supplementation with 30–60 mg elemental iron plus 400 µg folic acid during pregnancy to prevent several adverse outcomes. See the WHO recommendation. This global population recommendation should not be copied as an individual prescription: national strategies, anaemia prevalence and healthcare settings differ.

A recent Cochrane review, with evidence searched to January 2024, concludes that daily oral iron probably reduces iron deficiency and anaemia at term, while evidence is more uncertain for several other maternal and neonatal outcomes. Read the Cochrane summary. Distinguishing a well-supported effect on iron status from more uncertain clinical outcomes helps avoid exaggerated promises.

What does HAS recommend once deficiency or anaemia is diagnosed?

The HAS obstetric guidance uses oral iron as first-line treatment in the situations described, with follow-up to assess effectiveness. Therapeutic doses in the guideline are substantially higher than normal dietary intakes, which is precisely why they belong to prescribed treatment rather than general nutrition advice.

We deliberately do not turn those therapeutic doses into self-treatment instructions. If blood tests show an abnormality, the clinician managing the pregnancy determines whether treatment is needed, which formulation and dose to use, how long to continue it and when to repeat blood tests.

Why repeat blood tests?

Treatment cannot be assessed only by whether fatigue improves. HAS recommends checking effectiveness. If the expected response does not occur, clinicians can consider poor tolerance or adherence, inadequate absorption, another or additional cause, or a situation requiring a different strategy.

What adverse effects can oral iron cause?

Oral iron can cause nausea, abdominal discomfort, constipation, diarrhoea and dark stools. These recognised effects can make treatment difficult to continue. French National Health Insurance also highlights gastrointestinal adverse effects.

If constipation is already a problem, see our guide Constipation in pregnancy: understanding it and acting cautiously. Do not permanently stop a needed treatment simply because it causes constipation; discuss tolerance with the prescriber, who can reassess the strategy.

Nausea can also complicate treatment. Our article Nausea and vomiting in pregnancy: what to do and when to seek help covers cautious measures and warning signs. If vomiting prevents you keeping down food, fluids or medicines, tell your healthcare professional.

When is intravenous iron considered?

Intravenous iron exists but is not a convenience option to choose independently. HAS includes it in specific situations, including some cases of severe or poorly tolerated anaemia, intolerance of oral iron and some anaemias discovered late in pregnancy. The decision depends on gestational stage, severity, ferritin, tolerance and the time available before birth.

HAS assessments of intravenous ferric carboxymaltose more broadly note its use when oral preparations are ineffective, cannot be used or when there is a clinical need to deliver iron rapidly, with diagnosis based on appropriate laboratory testing.

Faster correction of some laboratory markers does not mean intravenous iron is preferable for every pregnancy. Clinical context and benefit-risk assessment guide the decision.

Vegetarian or vegan pregnancy: is extra monitoring needed?

A well-planned vegetarian diet can provide iron, although plant iron is generally less bioavailable. Variety, vitamin-C-rich combinations and appropriate monitoring therefore matter. A vegan diet also requires attention to other nutrients, particularly vitamin B12, independently of iron.

Risk is not identical for every vegetarian or vegan person. It depends on starting stores, dietary quality and other factors. Blood tests are more informative than assumptions based only on dietary label.

Multiple or closely spaced pregnancies

HAS includes multiple and closely spaced pregnancies among situations in which iron stores deserve particular attention. Greater cumulative requirements and less time to rebuild stores between pregnancies may contribute. This is a risk factor, not an automatic diagnosis.

Iron, fatigue and physical activity

Appropriate physical activity is generally encouraged in pregnancy when there is no contraindication, but symptomatic anaemia can affect exercise tolerance. If you are markedly breathless, weak or dizzy, or have received specific medical advice, do not push through symptoms to meet an exercise target. Our guide Physical activity in pregnancy: how much and which activities? explains why activity needs to be adapted to individual circumstances.

Can you diagnose deficiency by looking at eyelids, nails or skin?

No. Pallor can accompany anaemia, but looking at eyelids or nails cannot measure iron stores. Physical signs are too non-specific to replace a blood count and ferritin when testing is indicated. Social-media 'home tests' are not diagnostic.

Do prenatal supplements already contain iron?

Some do and some do not, and amounts vary. Before adding a separate product, check the composition of anything you already take and show it to the clinician managing the pregnancy. Combining supplements can produce unnecessary intake and make it harder to know what you are actually taking.

A food supplement and an iron-containing medicine may have different purposes and doses. A 'pregnancy' label does not mean a product can treat diagnosed deficiency.

Interactions and timing

Iron absorption can be affected by foods, supplements and medicines. Calcium, some antacids and other treatments may require separation depending on the exact product. A universal timing rule would be unsafe because formulations and co-medications differ.

Ask a pharmacist, midwife or doctor how to take the exact prescribed product, particularly if you use thyroid medication, antacids, antibiotics or several supplements.

What research can tell us — and what it cannot promise

The link between iron supplementation and improved iron status is well supported. The recent Cochrane review concludes that daily iron probably reduces anaemia and iron deficiency at term, but evidence is less certain for several other clinical outcomes affecting mother and baby.

FIGO published good-practice recommendations in 2025 emphasising screening and management of anaemia in pregnancy, including around childbirth. See the 2025 FIGO recommendations. International recommendations reinforce the importance of screening but do not replace French national protocols.

Statements such as 'iron will definitely prevent preterm birth' or 'low ferritin will definitely harm the baby' go beyond the evidence. Studies describe average risks and effects in populations; they cannot predict the outcome of an individual pregnancy with certainty.

Does a low result mean you ate badly?

No. Diet is only one part of the picture. Requirements rise, starting stores differ, and previous blood loss, closely spaced pregnancies, gastrointestinal conditions and other factors can contribute. Iron deficiency is not a judgement on the quality of someone's diet.

Conversely, eating a balanced diet does not make deficiency impossible. That is one reason laboratory screening exists.

When should you seek prompt medical advice?

Seek prompt medical advice for significant or unusual breathlessness, fainting, chest pain, marked palpitations, severe weakness, bleeding or deterioration in your general condition. During pregnancy, bleeding, unusual contractions, reduced fetal movements once movements are normally felt, severe pain or other concerning obstetric symptoms should be assessed independently of the iron question.

Persistent or severe fatigue also deserves discussion even when it is not an emergency, because iron deficiency is only one possible cause.

Useful questions for an antenatal appointment

• Is my haemoglobin normal for the obstetric guideline being used?
• Should my ferritin be measured or rechecked?
• Do these results actually indicate iron deficiency?
• Should another cause of anaemia be investigated?
• Does my prenatal supplement already contain iron?
• If treatment is needed, what dose and duration are planned?
• When should blood tests be repeated?
• What should I do if treatment causes nausea or constipation?
• Should iron be separated from another medicine or supplement?

Frequently asked questions

Does low ferritin automatically mean I am anaemic?

No. Iron deficiency can precede anaemia. Ferritin reflects iron stores, whereas haemoglobin is used in defining anaemia.

Can anaemia occur with normal ferritin?

Yes. Not every anaemia is caused by iron deficiency, and ferritin can be affected by inflammation.

Is fatigue enough reason to take iron?

No. Fatigue is non-specific. It can justify discussing symptoms and possibly testing, but not choosing treatment yourself.

Which foods are useful sources?

Thoroughly cooked meat, suitable fish, eggs, pulses, tofu, fortified cereals, seeds, nuts and vegetables can all contribute. Pregnancy food safety remains the priority.

Does vitamin C help?

It improves absorption of non-haem iron. This is useful nutritionally but is not sufficient treatment for significant diagnosed deficiency.

Must I stop tea or coffee?

Not necessarily. Intake should already respect pregnancy caffeine guidance. A clinician may advise separating them from an iron-rich meal or prescribed iron.

Does iron always cause constipation?

No, but constipation is a recognised adverse effect and tolerance varies.

Can the iron preparation be changed if I cannot tolerate it?

Different strategies exist, but changes should be discussed with the prescriber or pharmacist so treatment remains appropriate.

Is an infusion better than tablets?

It can correct some markers more quickly in selected situations, but it is not first-line for everyone. HAS defines specific indications.

Is iron dangerous for the baby?

The useful question is not whether iron is universally 'safe' or 'dangerous', but whether the right formulation and dose are being used for a genuine indication under appropriate care.

Should treatment continue after haemoglobin normalises?

Sometimes treatment is continued to rebuild stores. The individual duration should be confirmed by the clinician monitoring the blood results.

Does a vegetarian diet automatically require supplementation?

No. It increases the importance of a well-planned diet and appropriate monitoring, but treatment depends on individual context and results.

Why does my laboratory show a different normal range?

Laboratory reference intervals and clinical decision thresholds are not always the same. Methods and reference populations differ.

Does a twin pregnancy increase risk?

Multiple pregnancy is included by HAS among situations with increased risk of iron deficiency. That supports closer attention, not an automatic diagnosis.

Can diet alone prevent every deficiency?

No. In some people, increased requirements can exceed what diet alone can provide, particularly when starting stores are low.

Key points

Iron deficiency is common in pregnancy but should neither be trivialised nor self-diagnosed. Iron deficiency and anaemia are not synonyms. French HAS obstetric guidance uses defined criteria for screening and treatment. Diet contributes iron but may not replace treatment when deficiency or anaemia is confirmed. WHO global supplementation recommendations are public-health guidance and should not be converted into an individual prescription without considering the national and clinical context.

The most useful message is simple: do not infer your iron status from fatigue and do not copy someone else's dose. Have blood results interpreted, disclose supplements you already use and discuss adverse effects rather than silently stopping prescribed treatment.

Sources and references

• Haute Autorité de santé — Diagnosis and treatment of anaemia and iron deficiency in obstetrics, December 2025, tools updated in 2026, accessed 28 September 2026.
• Haute Autorité de santé — Patient blood management in surgery and obstetrics, updated March 2026.
• World Health Organization — Daily iron and folic acid supplementation during pregnancy, updated 2024.
• ANSES — Nutritional reference values for specific populations.
• NIH Office of Dietary Supplements — Iron: Health Professional Fact Sheet.
• French National Health Insurance — Definition and causes of iron-deficiency anaemia, 9 June 2026.
• French National Health Insurance — Symptoms and diagnosis of iron-deficiency anaemia, 9 June 2026.
• French National Health Insurance — Diet during pregnancy, 18 June 2026.
• Cochrane — Effects of daily oral iron supplementation during pregnancy, evidence current to 18 January 2024.
• FIGO — Good practice recommendations on anaemia in pregnancy, 2025.