Anaemia in pregnancy
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Anaemia in Pregnancy
Definition
The WHO defines anaemia in pregnancy as a haemoglobin (Hb) < 11 g/dL (at any trimester). In the UK/RCOG, < 10.5 g/dL is the threshold used in the second trimester. Severity is graded as:
| Grade | Hb (g/dL) |
|---|---|
| Mild | 10–10.9 |
| Moderate | 7–9.9 |
| Severe | < 7 |
Transfusion threshold: < 7 g/dL in pregnant patients, < 8 g/dL postpartum.
Note: Women with Hb 13–15 g/dL may actually reflect inadequate plasma volume expansion, also associated with low birthweight and preterm birth.
Physiological Changes in Pregnancy
A baseline understanding of pregnancy physiology is essential:
- Plasma volume expands 40–50% above baseline by weeks 16–24
- Red cell mass expands only 15–25% above baseline (from week 7)
- The net result is haemodilution → "physiologic anaemia of pregnancy" — a normocytic anaemia with Hb nadir at weeks 26–28
- Hb > 11 g/dL in late first trimester, or > 10 g/dL in second/third trimester → can be attributed to physiologic dilution without further investigation
- Hb below these thresholds, or microcytic/macrocytic anaemia, requires evaluation
(Goldman-Cecil Medicine; Creasy & Resnik's Maternal-Fetal Medicine)
Classification / Causes
Four types predominate in pregnancy:
- Iron deficiency anaemia (most common — 18% prevalence in the USA; IDA in ~5%)
- Folate deficiency
- Dilutional / physiologic
- Haemoglobinopathies (sickle cell disease, thalassaemia)
Other causes (less common in pregnancy):
- Aplastic anaemia
- Paroxysmal nocturnal haemoglobinuria (PNH)
- Autoimmune haemolytic anaemia
- B12 deficiency
- Anaemia of inflammation
Iron Deficiency Anaemia
Why demand is increased
- Expanding maternal red cell mass
- Fetal/placental iron demands (especially 3rd trimester)
- Blood loss at delivery
Adverse outcomes
- Mild–moderate IDA: ↑ preterm birth, low birth weight
- Severe IDA (Hb < 6–7 g/dL): fetal mortality, abnormal fetal oxygenation, PPROM, gestational hypertension, oligohydramnios
Diagnosis
Ferritin is the most sensitive and specific test:
| Test | Feature in IDA |
|---|---|
| Serum ferritin | ↓ (best single test; cutoff < 30 ng/mL: 92% sensitivity, 98% specificity) |
| Serum iron | ↓ |
| TIBC | ↑ |
| Transferrin saturation | ↓ |
| MCV | ↓ (microcytic) |
| Soluble transferrin receptor (sTfR) | ↑ (emerging marker) |
Note: Ferritin values are affected by haemodilution in later pregnancy. MCV, TIBC, and transferrin are less sensitive/specific than ferritin.
Reference ranges for pregnancy (Creasy & Resnik Table 55.1):
| Parameter | Normal Range |
|---|---|
| RBC | 2.72–4.55 × 10¹²/L (varies by trimester) |
| MCV | 81–99 μm³ |
| MCHC | 32–35 g/dL |
| Reticulocyte count | 48–152 × 10⁹/L (0.5–1.5%) |
| Serum ferritin | > 20 μg/L (first trimester: 72–143 μg/dL) |
Management — ACOG guidelines
| Severity | Treatment |
|---|---|
| Uncomplicated physiologic (no iron deficiency) | No treatment needed; good outcomes expected |
| Mild IDA (Hb 9–10.5 g/dL) | Oral non-enteric-coated supplemental iron |
| Severe IDA (Hb < 9 g/dL) in 2nd trimester | IV iron |
| Any IDA in 3rd trimester | IV iron preferred |
| 1st trimester | IV iron not used |
Oral iron dosing:
- A single daily dose is as effective as multiple-dose regimens and reduces GI side effects (GERD, constipation, nausea — already heightened in pregnancy)
- Intermittent dosing (2–3×/week) provides equivalent benefit with fewer side effects
- ACOG, WHO, and major authorities recommend ≥ 30 mg elemental (ferrous) iron daily during pregnancy
Prophylaxis:
- Routine supplementation reduces the risk of IDA at term even in women with normal Hb and iron stores
- Prevents postpartum iron deficiency
Folate Deficiency
- Macrocytic / megaloblastic anaemia
- Folate demand increases significantly in pregnancy (rapidly dividing cells)
- Neural tube defect prophylaxis: 0.4–0.8 mg/day folic acid pre-conception and through first trimester
- In countries with food fortification, the standard 0.8 mg/day dose is generally sufficient to prevent anaemia — higher doses needed if haemolysis, prior NTD pregnancy, antifolate medications, or malabsorption
- Women taking anticonvulsants or methotrexate may need 4–5 mg/day
Aplastic Anaemia in Pregnancy
- Can be diagnosed de novo in pregnancy or pre-existing
- Major complications: haemorrhage and sepsis (leading causes of maternal mortality)
- Other complications: PPH, abruption, pre-eclampsia, preterm delivery, FGR, fetal demise (especially if platelets < 20 × 10⁹/L)
- Management goals (supportive):
- Hb > 8 g/dL
- Platelets > 20 × 10⁹/L
- Treat infections aggressively
- RBC + platelet transfusions; cyclosporine; G-CSF; IVIG have been used
- Androgens are contraindicated in pregnancy (unless fetus confirmed male)
- Therapeutic abortion does not improve outcome — only indicated if marrow transplantation is urgently needed
- Modern supportive therapy: maternal mortality ≤ 15%
- Requires multidisciplinary team (haematology + anaesthesia + MFM)
(Creasy & Resnik, p. 1337–1338)
Sickle Cell Disease / Haemoglobinopathies
- Pre-conception Hb electrophoresis screening for populations at risk
- Pregnancy complications: vaso-occlusive crises, ACS, stroke, severe anaemia, preterm birth, FGR, IUFD
- Prophylactic transfusion or exchange transfusion may be considered
- Folate supplementation 5 mg/day recommended
Screening & Investigation Summary
Routine antenatal bloods:
- FBC at booking and 28 weeks
- Blood film if MCV abnormal
- Ferritin if Hb < 11 g/dL
- Hb electrophoresis (if indicated by ethnicity or MCV)
Further investigation if haemolytic anaemia suspected:
- Reticulocyte count, LDH, bilirubin, haptoglobin
- Direct Coombs test
- Blood film (schistocytes → TTP/HELLP)
- Flow cytometry (PNH)
- HPLC (haemoglobinopathies)
Key Maternal & Fetal Consequences of Untreated Anaemia
| Maternal | Fetal / Neonatal |
|---|---|
| Fatigue, palpitations, dyspnoea | Preterm birth |
| Reduced exercise tolerance | Low birth weight / SGA |
| Increased susceptibility to infection | Fetal iron deficiency → impaired neurodevelopment |
| Haemodynamic compromise in PPH | IUFD (severe anaemia) |
| Cardiac decompensation (severe) | Abnormal fetal oxygenation |
Recent Evidence
A 2024 Cochrane meta-analysis (PMID 39145520) on daily oral iron supplementation during pregnancy confirmed its efficacy in reducing maternal IDA and improving neonatal iron stores — supporting WHO and ACOG recommendations for routine prenatal iron supplementation.
Key sources:
- Creasy & Resnik's Maternal-Fetal Medicine, 9th ed., Ch. 55 (Haematologic Disorders)
- Goldman-Cecil Medicine, International ed., "Physiologic Anemia of Pregnancy"
- Rosen's Emergency Medicine, 9th ed., Ch. on Anemia in Pregnancy
- Harrison's Principles of Internal Medicine, 22nd ed.
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