Anaemia in pregnancy: symptoms, causes and treatment
Anaemia is one of the most common conditions encountered during pregnancy, and iron deficiency is by far the most frequent cause. The body's iron requirements increase considerably during pregnancy: iron is needed to produce haemoglobin for the expanded blood volume, to supply the developing baby and the placenta, and to prepare for the blood loss that occurs at delivery. When dietary intake and existing iron stores cannot keep pace with these demands, haemoglobin levels fall and anaemia develops. Understanding why this happens, what signs to look out for, and how it is treated can help you get the right support quickly if it affects you.
Why pregnancy increases the risk of anaemia
During pregnancy the total volume of blood in the body increases substantially to support the growing baby and placenta. This expansion means the body requires a much greater quantity of iron than usual to produce sufficient haemoglobin, the protein in red blood cells that carries oxygen. At the same time, the baby draws directly on the mother's iron stores for its own development, adding further to the demand. If dietary iron intake was already low before pregnancy, or if iron stores were depleted by a previous pregnancy, the gap between supply and demand can become significant. This is why routine blood tests during antenatal care specifically check haemoglobin levels and why the results are taken seriously even when symptoms are mild or absent.
Folate deficiency can also cause a form of anaemia in pregnancy, known as megaloblastic anaemia. This is a different mechanism from iron deficiency and is one reason why folic acid supplements are recommended before conception and in the first trimester. Both types of anaemia are screened for as part of routine antenatal blood tests.
How anaemia is detected
Anaemia in pregnancy is identified through a routine full blood count (FBC), which measures haemoglobin concentration and other components of the blood. This test is carried out at the booking appointment, typically between eight and ten weeks of pregnancy, and again at around 28 weeks. The 28-week check is particularly important because iron demands are greatest in the second and third trimesters, when the baby is growing rapidly and blood volume has expanded considerably.
According to NICE guideline NG25 on blood transfusion and the thresholds used in NHS antenatal care, a haemoglobin level below 110 g/L in the first trimester indicates anaemia. From 28 weeks onwards, the threshold is below 105 g/L, reflecting the haemodilution that occurs as blood volume increases faster than red cell mass. If your results fall below these thresholds, your midwife or GP will discuss the findings with you and recommend the appropriate next steps.
Recognising the symptoms
One of the challenges with anaemia in pregnancy is that its most common symptom, tiredness, is also a normal feature of pregnancy itself. Feeling fatigued in the first trimester is almost universal, and fatigue in the second and third trimesters is also common, so anaemia can be easy to overlook on the basis of tiredness alone. This is precisely why routine blood tests are so valuable: they provide an objective measure rather than relying on symptoms that are difficult to distinguish from ordinary pregnancy experience.
Alongside tiredness, other symptoms that may suggest anaemia include shortness of breath on minimal exertion, such as climbing a flight of stairs, pallor (a noticeably pale appearance, particularly around the inner eyelids and fingernails), heart palpitations and dizziness. None of these symptoms on their own confirm anaemia, and none should be ignored. If you notice any of them between routine appointments, mention them to your midwife or GP rather than waiting for the next scheduled check. A blood test can confirm or rule out anaemia quickly.
Treatment: iron supplements
The standard treatment for iron deficiency anaemia in pregnancy is oral iron supplementation, usually prescribed as ferrous sulfate, ferrous fumarate or ferrous gluconate. These are different salts of iron that vary in how well they are tolerated and absorbed, and your GP or midwife will advise on the most appropriate one for you. The aim of treatment is to restore haemoglobin levels to within the normal range and to rebuild iron stores before delivery.
There are several things that make a practical difference to how well the supplements work. Taking iron with a source of vitamin C, such as a small glass of orange juice, enhances absorption by helping to convert iron into a form the gut can take up more easily. Conversely, tea and coffee both contain compounds (tannins and polyphenols) that reduce iron absorption, so it is advisable to avoid them for at least an hour either side of taking your iron tablet. Calcium-rich foods and dairy products can also reduce absorption, so spacing iron away from large dairy meals is worth considering.
Side effects from oral iron supplements are common and include constipation, dark or tarry stools and nausea. Dark stools are a harmless result of unabsorbed iron and not a cause for concern. Nausea can sometimes be reduced by taking the supplement with food, although this may slightly reduce the amount of iron absorbed. Constipation can be managed with increased fluid intake, dietary fibre and, if necessary, a stool softener recommended by your GP. If side effects are severe or persistent, speak to your GP: switching to a lower dose or a different iron salt sometimes improves tolerability without sacrificing effectiveness.
When oral iron is not tolerated: intravenous iron
A small number of people find oral iron supplements impossible to tolerate due to persistent nausea, vomiting or severe gastrointestinal side effects. In these cases, or where anaemia is detected late in pregnancy and rapid correction is needed, intravenous (IV) iron infusion is an option. This involves iron being administered directly into a vein, usually in a day unit or outpatient setting, and can raise haemoglobin levels more quickly than oral supplements. Your doctor will advise whether IV iron is appropriate given your circumstances and the stage of your pregnancy.
Diet and iron-rich foods
While dietary changes alone are rarely sufficient to correct established iron deficiency anaemia in pregnancy, eating iron-rich foods can help support your iron levels and reduce the risk of deficiency developing. Iron in food comes in two forms: haem iron, found in meat and fish, is absorbed much more efficiently by the body; non-haem iron, found in plant-based foods, is absorbed less readily but can still make a meaningful contribution to overall intake.
Good sources of haem iron include red meat and oily fish. Plant-based sources of non-haem iron include lentils, chickpeas, kidney beans, tofu, dark green leafy vegetables such as spinach and kale, and fortified breakfast cereals. Eating non-haem iron sources alongside a food or drink rich in vitamin C, such as orange juice, tomatoes or bell peppers, can significantly increase the amount of iron absorbed from that meal. Conversely, drinking tea or coffee with meals is one of the most common reasons for poor iron absorption from food, so spacing hot drinks away from iron-rich meals is a straightforward way to get more from what you eat.
Frequently asked questions
How common is anaemia in pregnancy?
Iron deficiency anaemia is one of the most common conditions of pregnancy. The increased demands of the growing baby, placenta and expanded blood volume mean that many women develop at least mild anaemia, particularly in the second and third trimesters.
What are the symptoms of anaemia in pregnancy?
Tiredness is the most common symptom, but pregnancy tiredness is common generally, so anaemia can be easy to miss. Other signs include breathlessness on minimal exertion, pallor, heart palpitations and dizziness. A blood test is the reliable way to diagnose it.
How is anaemia treated in pregnancy?
The most common treatment is oral iron supplements prescribed by your GP or midwife, usually ferrous sulfate or a similar iron salt. Taking them with a small glass of orange juice improves absorption. If you cannot tolerate oral iron, an intravenous iron infusion is an alternative.
What foods are highest in iron?
Red meat and oily fish are the richest sources of haem iron, which the body absorbs most efficiently. Plant-based sources include lentils, chickpeas, beans, tofu, dark leafy vegetables and fortified breakfast cereals. Eating these alongside a source of vitamin C helps absorption.
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