Haemoglobin normally falls through the second trimester as plasma volume expands faster than red-cell mass, and iron stores are drawn down most heavily in the third trimester. A woman with a normal result at 10 weeks can reach delivery anaemic, and anaemia at that point is also the version that matters most for postpartum haemorrhage tolerance.
A repeat haemoglobin at about 28 weeks, and again near term where the first repeat was borderline, catches this while there is still time for oral or intravenous iron to work.
- Repeat haemoglobin at about 28 weeks for every woman
- Use pregnancy thresholds — below 11 g/dL in the first and third trimesters
- Pair a low result with ferritin where available
- Recheck two to four weeks after starting iron to confirm a response
Why it matters
The anaemia that develops late is the one least likely to be picked up and the one with least time to correct.
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