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OG12.2 | Anaemia in Pregnancy — SDL Guide

Learning Objectives

• Define anaemia in pregnancy and classify it by aetiology and severity using WHO criteria
• Describe the pathophysiology of iron deficiency anaemia in pregnancy including physiological anaemia
• Identify clinical features, investigations and diagnostic criteria for anaemia in pregnancy
• Explain the adverse effects of anaemia on the mother and foetus
• Outline the management of anaemia in pregnancy including prophylaxis, oral/parenteral iron, and transfusion

INSTRUCTIONS

Anaemia complicates approximately 50% of all pregnancies in India and is a leading indirect cause of maternal mortality. This module uses the OG disease arc to take you from recognising the clinical presentation through to evidence-based management, with a focus on the thresholds and drug choices that are tested in clinical exams and applied at the bedside.

References

• DC Dutta's Textbook of Obstetrics, 9th edition, Chapter 14 (textbook)
• Williams Obstetrics, 26th edition, Chapter 56 (textbook)
• WHO Guideline: Daily iron and folic acid supplementation during pregnancy, 2012 (guideline)
• NHM — Iron and Folic Acid Supplementation Programme, India (guideline)

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Version 2.0 | NMC CBUC 2024

Clinical Presentation of Anaemia in Pregnancy

Anaemia in pregnancy is defined by the World Health Organization (WHO) as a haemoglobin (Hb) concentration below 11 g/dL at any trimester of pregnancy. This threshold is lower than the non-pregnant female value of 12 g/dL because pregnancy causes physiological haemodilution — plasma volume expands by 40–50%, while red cell mass expands by only 20–30%, producing a dilutional fall in Hb that is normal and expected. The distinction between physiological haemodilution and true pathological anaemia is an important clinical judgment: a woman at 28 weeks with Hb 10.5 g/dL and a healthy peripheral smear may simply reflect normal dilution, whereas the same value with a microcytic hypochromic smear signals iron deficiency.

Clinically, pregnant women with anaemia present along a severity spectrum. Mild anaemia (Hb 10–10.9 g/dL) often produces no symptoms; it is detected only on routine antenatal screening. Moderate anaemia (Hb 7–9.9 g/dL) produces fatigue, exertional breathlessness, palpitations, easy fatigability, and mild pallor of the conjunctiva, tongue, and nail beds. Severe anaemia (Hb below 7 g/dL) causes resting dyspnoea, tachycardia, ankle oedema from a high-output state, and marked pallor; patients with haemolytic or haemorrhagic aetiology may be jaundiced. Very severe anaemia (Hb below 4 g/dL) is a medical emergency: congestive cardiac failure, pulmonary oedema, and imminent maternal collapse are immediate risks.

The epidemiological burden in India is staggering: the National Family Health Survey-5 (2019–21) reported that 52% of pregnant women aged 15–49 years are anaemic. Nutritional deficiency — primarily iron deficiency — accounts for approximately 95% of all anaemia in pregnancy in India, making it the dominant clinical problem in antenatal care. The remaining 5% includes folate/B12 deficiency, haemolytic anaemias (malaria, sickle cell, thalassaemia), and rare aplastic anaemia.

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On examination, key signs include conjunctival pallor (reliable below Hb 9 g/dL), pallor of the tongue and nail beds, koilonychia (spoon-shaped nails in iron deficiency), angular stomatitis, glossitis, and tachycardia. Fundal examination may reveal tortuous retinal vessels in severe chronic anaemia. Oedema, raised jugular venous pressure, and basal crepitations suggest cardiac decompensation.

Pathophysiology and Aetiology

Understanding why pregnancy generates a near-universal iron deficit requires tracing the simultaneous demands placed on maternal iron stores across all three trimesters. During a singleton pregnancy, the total additional iron requirement is estimated at 700–1000 mg: approximately 300 mg for foetal and placental development, 500 mg for expansion of the maternal red cell mass, and 200 mg to replace basal daily losses. The average Indian woman enters pregnancy with iron stores of only 200–300 mg — barely sufficient even for basal needs. When dietary intake (typically 10–15 mg/day with only 10% absorption) cannot bridge this deficit, iron deficiency develops and erythropoiesis becomes iron-restricted.

The sequence of iron deficiency progresses through three stages: first, iron depletion (falling serum ferritin, stores emptying); second, iron-deficient erythropoiesis (falling serum iron, rising TIBC, falling transferrin saturation, reticulocytes diminish); and third, frank iron deficiency anaemia (microcytic, hypochromic red cells; Hb falls below the WHO threshold of 11 g/dL). In practice, pregnant women often present at stage three because symptoms are insidious and early stages are asymptomatic.

Increased Iron Demand and Anaemia in Pregnancy

Classification by aetiology:
• Nutritional anaemia (most common — 95% in India):
- Iron deficiency anaemia (IDA): microcytic hypochromic; commonest cause; inadequate diet, poor absorption, recurrent infections (especially hookworm)
- Megaloblastic anaemia: macrocytic; folate deficiency (commonest megaloblastic cause in pregnancy — foetal and placental demands deplete folate rapidly) or rarely vitamin B12 deficiency
- Dimorphic anaemia: mixed iron + folate deficiency producing a mixed microcytic/macrocytic picture
• Haemolytic anaemia:
- Malaria: leading cause of haemolytic anaemia in endemic regions; also suppresses bone marrow
- Sickle cell disease / trait: more frequent crises in pregnancy; HbSS carries high perinatal mortality
- Thalassaemia: β-thalassaemia major presents before reproductive age; β-thalassaemia minor is the common carrier state detected incidentally
- Autoimmune haemolytic anaemia: rare in pregnancy
• Aplastic / hypoplastic anaemia: rare; idiopathic or drug-induced; poor prognosis for mother and foetus

Physiological anaemia of pregnancy must be differentiated from pathological anaemia. Plasma volume expansion begins at 6 weeks and peaks at 32 weeks; red cell mass expansion is slower and smaller, resulting in a nadir Hb around 28–32 weeks. This is NORMAL. A low Hb in a woman with a normal peripheral smear, normal MCV, normal iron studies, and no symptoms beyond fatigue represents physiological haemodilution, not iron deficiency, and should NOT trigger iron treatment beyond routine prophylaxis.

Investigations and Diagnosis

A systematic investigation approach is essential both to confirm the presence of anaemia and — critically — to identify its type, because the treatment differs fundamentally between iron deficiency, megaloblastic anaemia, and haemolytic disease.

The first-line investigation is a Complete Blood Count (CBC) with peripheral blood smear. The CBC provides Hb, haematocrit (PCV), red cell indices (MCV, MCH, MCHC, RDW), total white cell count, and platelet count. Mean Corpuscular Volume (MCV) is the key discriminator: MCV below 80 fL = microcytic (IDA, thalassaemia); MCV 80–100 = normocytic (early IDA, haemolytic, aplastic, anaemia of chronic disease); MCV above 100 fL = macrocytic (megaloblastic).

The peripheral blood smear adds morphological detail that the indices cannot fully capture, translating numerical values into visually recognisable patterns of red cell size, shape, and chromasia that directly reflect the underlying deficiency state:
- Iron deficiency: microcytic, hypochromic cells; pencil cells (elliptocytes); anisocytosis and poikilocytosis; high RDW
- Megaloblastic: macro-ovalocytes, hypersegmented neutrophils (≥5 lobes in ≥5% cells), elevated MCV; Howell-Jolly bodies in severe disease
- Dimorphic: mixed microcytic and macrocytic population; bimodal distribution
- Sickle cell: sickle-shaped erythrocytes, target cells, Howell-Jolly bodies
- Haemolytic: fragmented cells (schistocytes), spherocytes depending on cause

Iron studies provide definitive diagnosis of the type:

Parameter	Iron Deficiency Anaemia	Anaemia of Chronic Disease	Megaloblastic
Serum iron	Low	Low	Normal/High
TIBC	High (>360 µg/dL)	Low/Normal	Normal
Serum ferritin	Low (<12 ng/mL)	Normal/High	Normal
Transferrin saturation	Low (<16%)	Low	Normal
RBC folate	Normal	Normal	Low

Serum ferritin is the single best test for iron deficiency in pregnancy (below 12 ng/mL = depleted stores; below 30 ng/mL = probable deficiency in pregnancy context). However, ferritin is an acute-phase reactant and rises falsely in infection/inflammation — interpret with clinical context.

Additional investigations depending on clinical suspicion:
- Serum folate and vitamin B12: if MCV elevated or dimorphic picture
- Reticulocyte count: elevated in haemolytic anaemia; low in aplastic or nutritional
- Direct Coombs test (DAT): for autoimmune haemolysis
- Haemoglobin electrophoresis: if sickle cell or thalassaemia suspected (family history, Mediterranean/African origin, abnormal smear)
- Malarial parasite (MP) smear: thick and thin smear if febrile or in endemic area
- Urine microscopy: to exclude haematuria or haemoglobinuria
- Bone marrow examination: rarely needed; reserved for suspected aplastic anaemia or diagnostic uncertainty after full workup

Routine antenatal screening should include Hb measurement at booking (first visit), 28 weeks, and 36 weeks, supplemented by peripheral smear if Hb is below 11 g/dL.