Association between hematologic response to iron therapy and risk of stillbirth in pregnant singletons with moderate iron deficiency anemia.

Abstract

Background: Maternal iron deficiency anemia (iron deficiency anemia) is a persistent global health challenge with increased risk of adverse perinatal outcomes. A recent multicenter clinical trial found reduced rates of low birthweight infants in mothers treated initially (early second trimester) with IV ferric carboxymaltose compared to oral iron. Secondary findings included improved hematologic indices 4 weeks post-treatment, as well as reduced rate of stillbirth with single dose IV iron infusion.

Objective: We aimed to determine if the initial response to iron therapy was associated with risk of stillbirth and other adverse perinatal outcomes in pregnant singletons with moderate iron deficiency anemia STUDY DESIGN: This is a secondary analysis of a multi-center randomized controlled trial in India that compared single dose intravenous iron to oral iron for the initial management of moderate iron deficiency anemia (Hb 7.0-9.9g/dL) at 14-17 weeks gestation. The primary outcome for this secondary analysis is stillbirth. Secondary outcomes were early preterm birth <34 weeks, small for gestational age infants (<10%ile). The predictors of interest were maternal hemoglobin, ferritin, and transferrin saturation (TSAT), measured at 20-24 weeks gestation. Longitudinal hematologic and iron indices through pregnancy and association with outcomes were also assessed. Relative risk of each outcome based on post-treatment hemoglobin, ferritin, and TSAT was assessed with Poisson regression, adjusting for maternal age, BMI, parity, treatment modality, baseline Hb, and study site. Two-sided alpha=0.05 used for all analyses. Given that most nutrients exhibit U-shaped or threshold risk curves, we also fit models allowing for a quadratic function for the relationship between hematologic parameters at all times and risk of each event RESULTS: 4252 participants were included in this analysis, 1421, 1424, 1407 received intravenous ferric derisolmaltose, ferric carboxymaltose, and oral iron respectively. In evaluating the linear relationship, each unit of increasing Hb response at 20-24 weeks was significantly associated with reduced risk of stillbirth (RR 0.74 (0.56, 0.98). In evaluating the quadratic relationship, we found that there was a significantly progressively increased risk of stillbirth (p<0.0001) and early preterm birth< 34 weeks (p=0.01). Although there was a significant quadratic relationship identified with small for gestational age infant and Hb (p=0.008), the relative risk of SGA and lower Hb was not statistically significant.

Conclusion: Inadequate improvement in hemoglobin at 20-24 weeks following iron therapy in pregnancies complicated by moderate iron deficiency anemia is associated with increased risk of stillbirth and early preterm birth. Our findings highlight the potential importance of early screening and treatment of maternal anemia,. Given the association between persistent anemia at 20-24 weeks and adverse outcome, prospective trials should focus on whether early pregnancy, or even preconception, improvement in hemoglobin is an effective intervention to prevent adverse perinatal outcomes such as stillbirth and early preterm birth.