A target trial emulation study to estimate the causal effect of intravenous iron use during pregnancy and its effect on haematological and birth outcomes in Pakistan

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Abstract Background Despite several trials on the hematological outcomes of intravenous (IV) iron in pregnancy, only few have examined its effect on birth outcomes. We estimated the causal effect of IV-iron on moderate or severe anaemia and birth outcomes. Methods Women presenting to routine antenatal care in Pakistan with haemoglobin ≤10 g/dL were eligible for treatment. We used target trial emulation (TTE) methodology to estimate the effect of IV-iron treatment within 14 days of anaemia identification, compared to no treatment, on anaemia status at follow-up. A modified TTE analysis examined birth outcomes at delivery for singleton pregnancies, including birthweight, size-for-gestational-age, and mortality. We conducted a separate TTE for each of five gestational-age periods and pooled the results of each TTE. Results We screened 3115 pregnancies of which 1715 were eligible for IV-iron; 1043 participants were treated during pregnancy. Those who received IV-iron had half the risk of moderate or severe anaemia in pregnancy compared with no treatment (pooled relative risk (RR) 0.40; 95% confidence interval (CI): 0.27, 0.59). The pooled effect of IV-iron on stillbirth suggested an 83% risk reduction (95% CI 55-94%), and trends were similar for perinatal and neonatal mortality. Conclusion IV-iron treatment improved haematological status in pregnant women and was associated with a large reduction in stillbirth. Given limited data from randomised trials regarding fetal death and treatment earlier in pregnancy, this study contributes important information to the potential benefit of IV-iron in contexts where anaemia and its sequelae are a major public health problem. Key Messages Our research question was to assess if intravenous (IV) iron, compared with continued prophylactic oral iron alone, improves haematological and birth outcomes for those diagnosed with moderate or severe anaemia during pregnancy. The use of IV-iron for treatment of anemia in pregnancy during routine antenatal care settings may be more effective than continuing prophylactic dose of oral iron supplementation for improving hematological outcomes and reducing the risk of stillbirth, although there was no difference in the risk of preterm or low birth weight babies. Our study assessed the effect of treatment across the gestational age continuum, measured a comprehensive set of maternal and newborn health outcomes which were not studied in many clinical trials, and used data that reflects real world management of anemia where compliance to oral iron may be poor.

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