Anaemia is the most common medical problem of pregnancy, and the one most often summarised as "your iron is a bit low" without anyone explaining what that means. The World Health Organization estimates that 37% of pregnant women worldwide, around 32 million, were anaemic in 2019, and most of that is iron deficiency. Your blood volume rises by roughly half during pregnancy, plasma faster than red cells, so even a well-stocked body is diluted, and a body that started with low stores runs out.
This guide covers the numbers on your blood test and what they mean, the symptoms that are anaemia rather than ordinary pregnancy tiredness, how to take iron so it actually absorbs (most treatment failures are in the taking, not the tablet), and the point at which an infusion makes more sense than another month of pills.
The short answer. Anaemia in pregnancy means a haemoglobin below 110 g/L in the first trimester or below 105 g/L in the second and third (UK guidance; the WHO uses 110 again in the third). A ferritin below 30 µg/L means your iron stores are already low even if haemoglobin is still normal. The usual treatment is oral iron, taken as a single dose on alternate days, an hour or two away from tea, coffee and calcium, with a repeat blood test a few weeks later. Breathlessness at rest, chest pain or palpitations need a same-day call.
Why Pregnancy Uses Up Iron
1. Your blood is diluted
By the third trimester your plasma volume has risen by 45–55% while your red cell mass has risen by only 20–30%. The same red cells are floating in more fluid, so the concentration of haemoglobin falls even when nothing is wrong. That is physiological anaemia of pregnancy, and it is the reason the thresholds for a pregnant woman are set lower than for anyone else.
2. Two people are building blood
Your bone marrow makes extra red cells to carry oxygen for two. The baby builds its own blood and, in the last trimester, lays down iron stores to last its first months. The placenta needs iron too. All of it comes from your diet and your stores, and the birth itself costs blood on top.
3. Many women start low
Heavy periods before pregnancy, two pregnancies close together, a vegetarian or vegan diet without fortified foods, twins, or vomiting that stops you eating in the first trimester all mean the stores are thin before the demand even starts. A low ferritin at the booking bloods is very often iron that was missing before the pregnancy began.
Symptoms, and Why They Are Easy to Miss
| What you notice | Why anaemia does it | Also normal in pregnancy? |
|---|---|---|
| Tiredness rest does not fix | Less oxygen reaches your muscles and brain | Yes — see fatigue |
| Breathless on the stairs | Your lungs work harder to make up for fewer carriers | Yes — see shortness of breath |
| Palpitations, racing heart | The heart pumps faster to move the same oxygen | Sometimes |
| Dizziness, near-fainting | Less oxygen to the brain when you stand | Yes — see dizziness |
| Headaches | Same mechanism | Yes |
| Pale inside of the lower eyelids, pale nail beds | Fewer red cells under thin skin — the most useful home check | No |
| Restless legs at night | Iron deficiency is a known driver | Common, but worth a ferritin — see restless legs |
| Craving ice, or non-food things | Pica is specific to iron deficiency | No |
| Hair shedding, brittle nails, sore tongue, cracked mouth corners | Fast-turnover tissues run short of iron first | No |
The honest problem is that the first five rows are also what a normal pregnancy feels like. That is why the diagnosis is a blood test and not a symptom list, and why haemoglobin is checked at the booking appointment and again at around 28 weeks whether you feel anaemic or not.
Reading Your Blood Results
| Test | Anaemia or deficiency means | In g/dL |
|---|---|---|
| Haemoglobin, first trimester | Below 110 g/L | Below 11.0 |
| Haemoglobin, second trimester | Below 105 g/L | Below 10.5 |
| Haemoglobin, third trimester | Below 105 g/L in UK guidance; the WHO's 2024 cut-off is 110 g/L | Below 10.5 or 11.0 |
| Haemoglobin, after birth | Below 100 g/L | Below 10.0 |
| Ferritin | Below 30 µg/L = iron deficiency, with or without anaemia | Same units either way |
Ferritin is the number to ask about if your haemoglobin is borderline or you have symptoms, because it is not always part of the routine panel and it drops long before the blood count does. One caution: ferritin also rises with infection or inflammation, so a "normal" result during a bad cold can hide a real deficiency. Your doctor may check an inflammation marker alongside it for that reason.
The other red cell numbers on the report — MCV, MCH — are less reliable in pregnancy than outside it, because cell size rises naturally as the pregnancy goes on. A haemoglobin below 70 g/L is classed as severe anaemia and is treated urgently, not with a repeat prescription. The rest of the booking and 28-week panel is explained in our guide to pregnancy blood tests.
If your booking screen found a thalassaemia or sickle cell trait, a small red cell size on its own is not iron deficiency, and taking extra iron without a low ferritin can do harm rather than good. Treat the ferritin, not the cell size.
Treatment: How to Take Iron So It Works
Try this first: one tablet, once, on alternate days, an hour before or two hours after food, swallowed with water rather than tea, coffee or milk. Most iron courses that "did not work" were taken with breakfast tea every morning.
1. Which iron
Ferrous sulfate, ferrous fumarate and ferrous gluconate all work. The differences are in how much elemental iron each tablet carries and how well your stomach tolerates it, not in effectiveness, so a switch is the answer to side effects rather than stopping. The dose is your prescriber's decision; do not top it up with an over-the-counter product on your own.
2. Every other day, in one dose
Two small trials in women with depleted iron stores found that a single dose on alternate days was absorbed better than the same dose taken every day, and better than a daily dose split in two. The mechanism is a hormone called hepcidin: each dose of iron raises it for about a day, and while it is up the gut absorbs less from the next dose. Taking iron daily therefore fights itself. If you were prescribed daily dosing, ask whether alternate days would suit you — it usually also means fewer side effects.
3. What blocks it and what does not
Tea and coffee bind iron and cut absorption sharply; so do milk, calcium supplements and antacids. Keep them an hour or two either side of the tablet. Whole grains and bran matter less. Vitamin C is the one that surprises people: a randomised trial in adults with iron-deficiency anaemia found that adding 200 mg of vitamin C to oral iron made no meaningful difference to the haemoglobin rise at two weeks. Juice with the tablet is fine, but it is not the thing that decides whether the course works.
4. Side effects are managed, not endured
Nausea, stomach pain, constipation and a metallic taste are the common ones, and black stools are expected and harmless. If nausea is the problem, taking the tablet with a small amount of food loses some absorption but keeps you taking it, which matters more. If constipation is the problem, alternate-day dosing, more fluid and fibre, and a pregnancy-safe laxative usually solve it. A liquid preparation is the next step.
5. The recheck
Haemoglobin is rechecked a few weeks into treatment. If it has not risen, the questions are, in order: are the tablets actually going in, are they going in with tea, is something stopping absorption (a stomach-acid medicine, coeliac disease), or is this not iron deficiency at all. Once haemoglobin is back to normal, iron is continued for around three months to refill the stores, and until at least six weeks after the birth.
6. When it is an infusion instead
Intravenous iron is used when tablets are not tolerated or have failed after a proper trial, when the anaemia is severe, or when the birth is close enough that tablets cannot work in time. It is given in hospital from the second trimester onwards and refills the stores in one or two sessions. It is a fallback, not an upgrade: for most women, tablets taken properly do the job.
Iron on the Plate
What actually delivers iron
- Haem iron, absorbed best: lean red meat, the dark meat of poultry, and well-cooked fish such as sardines. Safe choices are in our can-I-eat guide.
- Non-haem iron: lentils, chickpeas, beans, tofu, fortified breakfast cereals, dried apricots, pumpkin seeds. Absorbed less well, so eat more of it and pair it with the next line.
- Vitamin C at the meal: peppers, tomatoes, citrus, kiwi, berries. This is where vitamin C earns its place — with plant iron on the plate, not as a pill beside the tablet.
- Eggs and green vegetables add a little; do not count on spinach alone.
- Liver and liver pâté. Rich in iron and off the list in pregnancy because of vitamin A — see liver in pregnancy.
- Tea or coffee with the meal. Have it an hour later.
Diet alone rarely reverses an anaemia that has already developed in pregnancy, because the daily demand is higher than food can comfortably supply. What diet decides is whether you keep the gain once the course of tablets ends.
Prevention: Should Everyone Take Iron?
Two sensible bodies give two different answers, and both are right for the population they are looking at. The WHO recommends 30–60 mg of elemental iron daily, with folic acid, for all pregnant women, because in much of the world anaemia in pregnancy is common enough that testing everyone first is not practical. A Cochrane review of 14 trials in 2,199 women found that preventive daily iron cut anaemia at term by 70%.
UK guidance goes the other way: no routine iron for everyone, but a blood test at booking and at 28 weeks, and treatment for anyone who needs it. Most prenatal multivitamins carry a modest dose either way. If you are at higher risk — a previous anaemia, heavy periods, twins, a short gap since your last pregnancy, a diet without meat — ask at booking whether you should start earlier rather than wait for the 28-week result.
When to Call Your Doctor
Call the same day if: you are breathless at rest or lying flat, have chest pain, palpitations that do not settle, or faint; if you have any bleeding; or if a result shows a haemoglobin below 70 g/L, which is severe anaemia and is treated urgently. Do not wait for the next routine appointment for any of these.
Do not start a high-dose iron product on your own because you feel tired. Get the blood test first: tiredness has other causes in pregnancy, and iron you do not need is not harmless.
At a Glance
Around 37% of pregnant women worldwide are anaemic, and most of it is iron deficiency made worse by the normal dilution of pregnancy. The thresholds are 110 g/L in the first trimester and 105 g/L after it, with ferritin under 30 µg/L meaning deficiency even before the haemoglobin drops. Take oral iron as a single dose on alternate days, away from tea, coffee and calcium; expect black stools, manage constipation rather than stopping, and get the recheck done. Vitamin C tablets add little, liver is off the menu, and an infusion is the fallback when tablets fail or time is short. Breathlessness at rest, chest pain or fainting mean a call today.
Inside Baby Novum. The lab results journal keeps every haemoglobin and ferritin reading in one dated list with a photo of the printed report, so the 28-week result sits next to the booking one at the appointment. The supplement tracker has iron in its built-in library, sends a reminder at the time you choose, and shows an adherence bar — which answers the "are the tablets actually going in" question before your doctor asks it.
Next: Pregnancy Blood Tests → · Prenatal Supplements → · Constipation Relief →
Frequently Asked Questions
How common is anaemia in pregnancy?
The World Health Organization estimates that 37% of pregnant women worldwide — around 32 million — were anaemic in 2019, and most of it is iron deficiency. Where antenatal blood tests are routine it is usually caught at the booking bloods or the 28-week repeat, which is exactly why those two tests exist.
What haemoglobin level counts as anaemia in pregnancy?
UK guidance uses a haemoglobin below 110 g/L in the first trimester, below 105 g/L in the second and third, and below 100 g/L after birth. The WHO's 2024 cut-offs are 110 in the first and third trimesters and 105 in the second. Your report may print it in g/dL instead: 11.0, 10.5 and 10.0.
What is a normal ferritin level in pregnancy?
Ferritin measures your iron stores, and it falls before haemoglobin does. A ferritin below 30 µg/L means iron deficiency even if your haemoglobin is still normal, and UK guidance treats it. A normal haemoglobin with a low ferritin is the most common pattern in early pregnancy — the stores are going before the blood count shows it.
Should I take iron every day or every other day?
Two small trials in women with low iron stores found more iron was absorbed when a single dose was taken on alternate days than when the same dose was taken daily or split into two, because a daily dose raises the hormone hepcidin and blocks the next one. Many clinicians now suggest alternate-day dosing. Follow what was prescribed, and ask before changing it.
Do I need to take vitamin C with iron tablets?
Not as a supplement. A randomised trial in adults with iron-deficiency anaemia found that adding 200 mg of vitamin C to oral iron made no meaningful difference to how fast haemoglobin rose. A glass of orange juice does no harm, but keeping tea, coffee and milk an hour or two away from the tablet matters more.
Iron tablets make me constipated. Can I stop taking them?
Not without asking — untreated anaemia costs you more than constipation does. Ask about alternate-day dosing, a different iron salt, or a liquid preparation, and treat the constipation itself with fibre, fluids and a pregnancy-safe laxative if you need one. Black stools while you are on iron are normal and not a reason to stop.
Can anaemia in pregnancy harm my baby?
Mild anaemia that is being treated is not something to add to your list of worries. Left untreated, more severe anaemia is associated in studies with low birth weight and preterm birth, and it leaves you less able to cope with the normal blood loss of birth. That is why it is treated rather than watched.
When is IV iron used in pregnancy?
When oral iron is not tolerated or has not worked after a proper trial, when the anaemia is severe, or when there is not enough time before the birth for tablets to work. It is given as an infusion in hospital, from the second trimester onwards, and it is a fallback rather than a first choice.
Sources
- WHO — Anaemia fact sheet
- British Society for Haematology — UK guidelines on the management of iron deficiency in pregnancy
- Cochrane — Daily oral iron supplementation during pregnancy
- The Lancet Haematology — Iron absorption from oral iron supplements given on consecutive versus alternate days
- JAMA Network Open — The efficacy and safety of vitamin C for iron supplementation in iron deficiency anaemia
- WHO eLENA — Daily iron supplementation during pregnancy
- StatPearls — Physiology, Maternal Blood
- NHS — Vitamins, supplements and nutrition in pregnancy