Moderate anaemia in an Indian antenatal clinic is so common that it is treated almost reflexively: haemoglobin low, iron prescribed, next patient. That works for the majority, and it quietly fails the minority in whom iron is not the answer — who are precisely the women whose haemoglobin will not rise, and who today's lead finding identifies as being at higher risk.
Before accepting iron deficiency as the diagnosis, check that the picture fits. A low mean corpuscular volume with low ferritin is straightforward. A normal or high mean corpuscular volume points elsewhere — B12 or folate deficiency, which is common in vegetarian populations and is not treated by iron. A microcytic anaemia with normal or high ferritin, or one that does not respond, raises thalassaemia trait and haemoglobinopathy, which matter for the pregnancy in a different way entirely: the partner needs testing, and the fetus may be at risk. Ferritin is an acute phase reactant, so a normal value in the presence of infection or inflammation does not exclude iron deficiency.
The other half is why she is deficient. Ask about menorrhagia before this pregnancy, short interpregnancy interval, hookworm exposure, and diet. And check adherence honestly — oral iron causes enough gastrointestinal upset that many women stop it without saying so, and 'not taking it' is a far commoner reason for non-response than any of the diagnoses above.
- Check the mean corpuscular volume before assuming iron deficiency; a normal or high value points to B12 or folate.
- Non-response to iron should prompt testing for thalassaemia trait and haemoglobinopathy, with partner testing.
- Remember ferritin rises with inflammation, so a normal value does not exclude iron deficiency.
- Ask about adherence and gastrointestinal side effects first — it is the commonest reason for non-response.
- Look for the cause: menorrhagia, short interpregnancy interval, hookworm, dietary restriction.
The statistics, in plain English
The diagnostic difficulty here is that the two commonest causes of microcytic anaemia in this population — iron deficiency and thalassaemia trait — frequently coexist, and each masks the other's laboratory signature. Ferritin is the most useful single test but behaves as an acute phase reactant, so its performance drops sharply where infection and inflammation are common. That is why the response to treatment carries diagnostic information: a haemoglobin that does not move with adequate iron is itself a test result, and today's data suggest it is one that also predicts outcome.
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