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

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

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

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)]).

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.

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