The benefits and harms of oral iron supplementation in non-anaemic pregnant women: A systematic review and meta-analysis

Preprint

Objective Iron deficiency during pregnancy poses a significant risk to both maternal and foetal health. Despite increased iron requirements during pregnancy, current UK NICE guidelines do not give clear advice on antenatal iron supplementation for non-anaemic women. We aimed to assess whether the benefits of routine antenatal supplementation outweigh potential harms for non-anaemic women.

Methods The Cochrane Library, MEDLINE, Embase and clinical trial registries were searched for randomised control trials (RCTs) and observational studies comparing oral iron supplementation with placebo or no supplement in non-anaemic pregnant women. The relevant data were extracted, and the risk of bias for included studies was assessed using the Cochrane Risk of Bias tool and the Newcastle-Ottawa Scale. Where appropriate, meta-analysis was conducted using ‘R’.

Results 23 eligible studies were identified including 4492 non-anaemic women who were followed through pregnancy. Haemoglobin and ferritin levels were consistently higher in individuals receiving iron compared with control groups, although both findings were associated with a high degree of heterogeneity (I2 = 92% and 87% respectively) and therefore did not warrant a pooled analysis. Iron supplementation was associated with a significant reduction in rate of maternal anaemia (OR = 0.36; 95% CI = 0.22 - 0.61, p<.001; I2 = 54%; moderate certainty, NNT 8). There was no significant effect of intervention on birth weight (MD = 22.97g, 95% CI = -56.27 to 102.22, p = 0.57; I2 = 64%; very low certainty). Of the 18 studies reporting adverse effects, none found a significant influence of supplementation on GI disturbance, caesarean sections or preterm births.

Conclusions Prophylactic iron supplementation reduces the risk of maternal anaemia in pregnancy. Limited evidence was found relating to the harms of supplementation in non-anaemic pregnant women, highlighting the need for further research to inform practice guidelines and support clinical decision making.

Registration The study protocol was registered on the Open Science Framework (DOI 10.17605/OSF.IO/HKZ4C).

Authors: Watt, A; Eaton, H; Eastwick-Jones, K; Thomas, E; Pluddemann, A

• Publication status: Published
• Peer review status: Not peer reviewed
• Preprint server: medRxiv
• Publication date: 2024-02-13
• DOI: 10.1101/2024.02.13.24302756
• Language: English
• Keywords: pregnancy outcome; pregnancy; anemia; iron-deficiency / prevention and control; newborn; dietary supplements; adverse effects; folic acid / administration and dosage; humans; infant; low birth weight; iron / administration and dosage; iron; dietary / administration and dosage; pregnancy complications; prenatal care / methods; hematologic / prevention and control