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

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.