Case 125 – Summary

Thanks for all your input in managing this case or iron deficiency anaemia in pregnancy.   Case 45 previously discussed anaemia in pregnancy and this case highlights changes in recommendations for oral iron replacement as well as indications and complications associated with intravenous iron.

Blood parameters and pregnancy

In pregnancy there is a physiological reduction in haemoglobin due to the dilutional effect from expansion of plasma volume as well as increased use of iron for foetal growth and maternal erythropoiesis. As such there are different thresholds used to define anaemia in pregnancy which are:

  • Hb <110 g/l in the first trimester
  • Hb <105 g/l in the second and third trimester 
  • Hb< 100g/L immediately postpartum

Other factors which may contribute towards anaemia are many and include iron, vitamin B12 and folate deficiency, haemoglobinopathies,  inflammatory disorders, haemolysis and bleeding.

Other changes to blood parameters which occur in pregnancy include a 20% increase in red cell mass with increase in MCV of up to 6fL, which may mask the reduced MCV which may be seen in iron deficiency. There may be a neutrophilia and monocytosis. The blood film may be left shifted. 

Risks of iron deficiency in pregnancy

Risks to the mother which may be associated with iron deficiency include fatigue, increased infection, reduced cognition, postpartum haemorrhage and possible need for blood transfusion.

Risks to the baby may include increased perinatal and neonatal mortality, pre‐term birth and low birth weight and less clear cut – possible neurodevelopmental issues. Haemoglobinopathy screening

Haemoglobinopathy screening

All pregnant women are offered a FBC and group and save as well as screening for haemoglobinopathy via the family origin questionnaire at their booking appointment (usually 8-12 weeks). All women in high risk areas (foetal prevalence of sickle cell disease >1.5/10 000) will have a haemoglobinopathy screen as well as those with risk identified from their family origin questionnaire and blood count. The screening programme looks for sickle cell disease, thalassaemia and some unusual haemoglobin variants.  It is not designed to pick up HbH disease in the foetus, although it may do.  

Oral iron replacement

If the routine blood count shows microcytic anaemia it is reasonable to assume this is due to iron deficiency and give a trial of iron whilst awaiting a haemoglobinopathy screen. If there is evidence of haemoglobinopathy, check a ferritin level before starting a trial of iron to avoid exacerbating iron overload.

Recent BSH guidelines for iron deficiency in pregnant women now recommend 40-80mg of elemental iron daily as once daily dosing or alternate day dosing has been found to lower hepcidin levels and maximise fractional absorption of iron whilst reducing adverse effects.  Daily dosing is suggested as a practical compromise aiming for optimum compliance and more rapid response. Alternate day dosing is suggested if nausea and epigastric discomfort is experienced. 

To optimise use of oral iron:  

  • Take with vitamin C to increase absorption
  • Take early in the morning on an empty stomach
  • Warn about potential adverse effects and how to manage them
  • Avoid taking with tannins (tea, red wine etc.)
  • Don’t take with PPIs or H2 receptor blockers

After starting oral iron treatment, the full blood count should be checked at 2-3 weeks and should demonstrate a rise in Haemoglobin if the anaemia is due to iron deficiency.

Once the Hb is in the normal range, replacement should continue for 3 months and until at least 6 weeks postpartum to replenish iron stores.

IV iron replacement

Consider IV iron replacement if:

  • Unable to tolerate different preparations of oral iron
  • Need quick increase in haemoglobin e.g. nearing delivery. BSH guidelines suggest it should be considered in women presenting after 34 weeks gestation with confirmed iron deficiency anaemia and an Hb of <100 g/L
  • No response to oral iron/malabsorption issues

IV iron is contraindicated in the first trimester and can rarely cause transient fetal bradycardia so the manufacturers recommend monitoring of the foetus during administration. It is also contraindicated in bacteraemia or decompensated liver disease or if there is a history of anaphylaxis or serious hypersensitivity following any IV iron preparation and suggested use with caution. The manufacturers recommend monitoring for 30 minutes after the infusion for any reactions, although the risk is low (<1/200,000). Extravasation can cause haemosiderin skin staining which may be permanent and any discomfort at the infusion site should be reviewed, the infusion stopped, and plastics advice sought if concern.

When to refer to specialist care

BSH guidelines recommend referral to specialist care if Hb <70 g/L and/or associated with significant symptoms or gestation >34 weeks, or if the Hb is failing to respond after 2–3 weeks of oral iron correctly taken. They state that iron deficiency anaemia should not affect decisions on the mode of delivery, but anaemia is associated with increased risk of PPH, hence women with Hb <100 g/l approaching birth should have an individualised plan. This should include consideration of IV access, birth in an obstetrician‐led unit and active management of third stage of labour.

Women with uncorrected anaemia antenatally should have a Hb check within 48 h of birth, as should those who have had blood loss >500 ml, or symptoms suggestive of postpartum anaemia.

References:

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