Approaches for optimising intravenous iron dosing in pregnancy: a retrospective cohort study.

Background: Intravenous iron is commonly utilised in pregnancy when treatment with oral is not tolerated or where rapid replenishment of iron stores is required.

Aims: To examine the relationship between doses of intravenous iron administered during pregnancy according to different maternal bodyweight measures and subsequent treatment response.

Methods: Retrospective cohort study of pregnant women with confirmed iron deficiency anaemia who received intravenous iron polymaltose at a tertiary teaching hospital in Australia from 1 January 2014 to 31 January 2016. Diagnosis of anaemia and/or iron deficiency, infusion dosage characteristics and haematological parameters were collected from paper-based case notes and electronic records. The dose of intravenous iron administered was examined relative to maternal total bodyweight (TBW), ideal bodyweight (IBW) (equation = 45.5 kg + 0.9 kg/cm for each cm over 152 cm) and adjusted bodyweight (equation = IBW + [0.4 × (TBW - IBW)]).

Results: A total of 122 pregnancies was identified where women had confirmed iron deficiency anaemia and received a single infusion of intravenous iron polymaltose. Dose-response relationships were evident between change in haemoglobin from treatment until delivery and intravenous iron dose according to adjusted bodyweight (adjusted beta coefficient 0.70 (95% CI 0.24-1.15)) and pre-pregnancy total bodyweight (adjusted beta coefficient 0.83 (95% CI 0.36-1.29)), but not ideal bodyweight (adjusted beta coefficient 0.37 (95% CI -0.04-0.78)). Calculating iron deficit using adjusted bodyweight most closely matched that based on a physiological estimate of iron deficit according to weight-based total blood volume.

Conclusion: Optimal treatment outcomes in pregnant women requiring intravenous iron may be reached by dosing according to adjusted pre-pregnancy bodyweight rather than ideal bodyweight.