Background: Iron deficiency during pregnancy poses a significant risk to both maternal and foetal health. Current international guidelines provide discrepant advice on antenatal iron supplementation for non-anaemic women.
Objective: We aimed to quantify the benefits and harms of routine antenatal supplementation in non-anaemic women.
Methods: The Cochrane Library, MEDLINE, Embase, and clinical trial registries were searched for randomized controlled trials and observational studies comparing oral iron supplementation with placebo or no supplement in non-anaemic pregnant women. Risk of bias was assessed for each study and the results were synthesized via meta-analysis.
Results: Twenty-three eligible studies were identified with 4492 non-anaemic pregnant women. Supplemented groups had higher haemoglobin [mean difference = 6.95 g/l, 95% confidence interval (CI): 4.81-9.09, P < .001, moderate certainty, I2 = 91%] and ferritin (mean difference = 12.22 ng/ml, 95% CI: 6.92-17.52, P < .001, moderate certainty, I2 = 87%) and were at lower risk of anaemia (relative risk = 0.50, 95% CI: 0.34-0.74, P < .001, high certainty, I2 = 42%, number needed to treat (NNT) = 10). There was no difference in birth weight, preterm birth, and rate of caesarean section. Reporting on harms was inconsistent and there was insufficient evidence to determine an association between iron supplements and any negative outcome.
Discussion: Prophylactic iron supplementation likely results in a large reduction in maternal anaemia during pregnancy. Future research should qualify the impact of this benefit on women's quality of life and determine which subpopulations benefit most. Evidence surrounding the harms of iron supplementation in the non-anaemic population is poor quality and inconsistent. Randomized controlled trials quantifying the risk of gastrointestinal (GI) disturbance and iron overload are essential to inform iron supplement use and reduce unwarranted variations in international guidelines.
Keywords: anaemia; care; iron; iron deficiencies; pregnancy; prenatal.
During pregnancy, women need extra iron to help produce more red blood cells for themselves and the developing foetus. Around one in five women do not get enough iron during pregnancy and develop iron-deficiency anaemia (IDA), which can lead to tiredness, shortness of breath, premature birth, and low birth weight. The World Health Organization advises all pregnant women take iron supplements. However, iron supplements can cause side effects including nausea, constipation, and diarrhoea, leading some countries to recommend them only for women who have already developed anaemia due to iron deficiency. Our review aimed to identify the benefits and harms of iron supplements for women who do not already have anaemia, since previous reviews have not looked specifically at this group. We found iron supplements reduce the risk of developing anaemia and estimated that supplementation prevents one case of anaemia for every ten women who take them. This review identifies potential avenues for future research, particularly the need for more research into the harms of iron supplements in women who do not already have anaemia. This would help inform clinical guidance and allow women to determine whether iron supplements are right for them.
© The Author(s) 2025. Published by Oxford University Press.