Anaemia in pregnancy


Haemodilution in pregnancy is a normal physiological process that leads to a fall in haemoglobin (Hb) due to an increase in plasma volume. It is acceptable for a woman’s Hb to decrease down to as low as 105g/L during pregnancy. Fetal complications such as growth restriction and preterm birth are related to low Hb (rather than low iron stores with a normal Hb), and are rare if the haemoglobin is >90g/L, and only start to become significant if the Hb drops below 70-80g/L. Interestingly, there is no good evidence that iron supplementation reduces poor outcomes in severe iron deficiency.

Full blood count at booking

The rationale for doing a full blood count at booking is to screen for iron deficiency and haemoglobinopathies (which are becoming more common as our population becomes more diverse).

  • A normal Hb > 110 g/L and an MCV > 80 will generally rule out iron deficiency and haemoglobinopathies at booking and no additional testing is required at that point.
  • Routine iron supplementation for all women in pregnancy is not recommended, and routine iron studies for all women are not recommended if the FBC parameters are normal.

If iron deficiency is suspected, checking ferritin is usually all that is required for well pregnant women. Ferritin is an acute phase reactant however and the results can be difficult to interpret in acute and chronic illnesses, but for most well pregnant women it will be sufficient.

  • Ferritin levels <30ng/mL indicate a low iron status and
  • Ferritin levels <15ng/mL indicate depletion of iron stores.

Women at risk of iron deficiency include:

  • Multigravidas with a short gap between pregnancies
  • Multiple pregnancy
  • Adolescent women
  • Previous history of iron deficiency
  • Poor socio-economic status
  • Vegetarians or vegans,
  • Previous PPH in recent pregnancy,
  • History of malaria or hookworm.

If the Hb drops to below 105g/L at 28 weeks, it is reasonable to assume iron deficiency if a haemoglobinopathy has previously been ruled out, or their demographics make this very unlikely (eg a white Caucasian woman). Simply instituting oral iron replacement is reasonable without iron studies. Checking the ferritin will of course confirm the diagnosis. A repeat full blood count at 34-36 weeks is worthwhile for these women to assess their response to oral iron supplementation.


Oral supplementation is first line treatment, and when instituted after the booking or the 28 week full blood count will usually ensure adequate time to replenish iron stores by full term.

  • Women should take oral iron supplementation on an empty stomach, one hour before meals, with a source of Vitamin C (ascorbic acid) such as orange juice to maximise absorption.
  • Other medications or antacids should not be taken at the same time.
  • Side-effects of iron supplementation include diarrhoea, constipation and nausea.
  • Care should be taken with foods that inhibit the absorption of haem iron, these include calcium in dairy products, tea and coffee, chocolate, soy products and bran cereals, and also medications such as anticonvulsants, sulphonamides and medications that raise gastric pH i.e. antacids, H2-receptor antagonists.
Iron infusions in pregnancy

Iron infusions in pregnancy are second line treatment and should be reserved for women who have failed oral iron supplementation, or when iron deficiency is diagnosed late term when there may not be enough time for oral replacement.

We would usually only recommend an iron infusion if the haemoglobin is <90g/dL and the ferritin is less than 15 ng/mL, as pregnancy complications are rare if the parameters are higher than that. Although they are seen to be safe and are efficacious, it is a large dose of iron delivered relatively quickly and a recent report has suggested that side effects are not uncommon (up to 25 per cent).

Don’t forget that we can always give an iron infusion in hospital in the postnatal period if there is any doubt.

Options for iron infusion are Iron Polymaltose or Iron Carboxymaltose (Ferinject®). Note that Iron Carboxymaltose (Ferinject®) is not available on the hospital formulary, and women will need to source if from a pharmacy with an outside script and bring it in with them for administration as an outpatient through the ambulatory care unit.

pdf Click here (48 KB) to view the elemental Iron content of common preparations available.