Anaemia in Pregnancy
BSH UK guidelines on the management of iron deficiency in pregnancy. Last reviewed: Jan 2021.
Definition
Specific Hb thresholds are used to define anaemia during and after pregnancy:
| Timing | Hb threshold (g/L) |
|---|---|
| 1st trimester | <110 |
| 2nd and 3rd trimester | <105 |
| Postpartum | <100 |
Aetiology
| Physiological haemodilution | During pregnancy, there is a physiological increase in plasma volume
However, the increase in plasma volume exceeds the increase in RBC production → dilutional drop in haemoglobin concentration |
| Nutritional and medical causes |
|
| Factors increasing risk of iron deficiency |
|
Clinical Features
Anaemia symptoms are non-specific in pregnancy, as they often overlap with the normal physiological changes of pregnancy.
For example, fatigue, dizziness, and shortness of breath are common experiences in healthy pregnancies.
| Non-specific anaemia features | Symptoms:
Signs:
|
| Features specific to iron deficiency anaemia |
|
Investigation and Diagnosis
The primary goal of investigations is to confirm iron deficiency – the most common cause of anaemia in pregnancy
- Routine FBC is performed at the booking appointment (8-12 weeks)
In pregnancy, there are 2 ways to diagnose iron deficiency:
- Low haemoglobin + low serum ferritin
- Haemoglobin thresholds: <110 g/L in 1st trimester; <105 g/L in 2nd and 3rd trimester
- Note that a normal or high ferritin level does not rule out iron deficiency, as ferritin is an acute-phase protein that rises due to physiological changes or inflammation
- Diagnostic oral iron trial
- Patients with anaemia but have no obvious other cause (e.g. normal ferritin) should be offered a trial of iron immediately
- An increase in haemoglobin 2-3 weeks after confirms iron deficiency
Key laboratory findings in iron deficiency anaemia:
| Investigation category | Findings in IDA |
|---|---|
| FBC | Microcytic, hypochromic anaemia
↓ / Normal reticulocyte count |
| Iron studies |
|
| Peripheral blood smear |
|
Management
Dietary Advice
While diet alone CANNOT replenish iron stores once a woman is already iron-deficient, education can help improve intake and absorption:
- Haem iron (from meat, fish, and poultry) is absorbed more easily than non-haem iron
- Vitamin C enhances the absorption of non-haem iron
- Tannins in tea and coffee inhibit absorption and should be AVOIDED during or shortly after meals
Iron Supplementation
There are 3 main indications for oral iron supplementation for anaemia in pregnancy:
| Indication/ scenario | Description / notes |
|---|---|
| Confirmed iron deficiency anaemia | In pregnancy, iron deficiency anaemia can be confirmed with:
|
| Anaemia with no obvious other cause | This applies to those with low haemoglobin (see definition section for thresholds), but who are not diagnosed with iron deficiency or other causes A diagnostic trial of oral iron should be started immediately
|
| High-risk women | Prophylactic / empirical oral iron supplementation should be offered to high-risk women:
|
For women with a known haemoglobinopathy (like thalassaemia), check serum ferritin before starting iron to confirm deficiency and avoid potential iron overload.
IV Iron Therapy
Key indications for IV iron therapy:
- Oral iron intolerance of non-compliance
- Poor response to oral iron
- Malabsorption
- Need for rapid haemoglobin correction
- >34 weeks of gestation with confirmed iron deficiency anaemia
- Rationale: a rapid haemoglobin correction is necessary as the woman approaches delivery
- Oral iron typically takes 2-3 weeks to have a response which may not provide enough time to correct the anaemia before birth
IV iron is contraindicated during the first trimester of pregnancy and should only be considered from the second trimester onwards