Does taking iron in pregnancy help, and how much of it reaches the baby?

Iron in pregnancy does one thing reliably and several things marginally. It prevents and treats anaemia, which is the outcome every trial agrees on. Beyond that the picture thins out fast: a small reduction in small babies, no clear change in preterm birth, no measurable effect on maternal deaths in the trials that looked. That gap between a strong blood result and a weak birth result is the whole subject of this page.

Established. Iron deficiency anaemia in pregnancy is real, common and worth preventing. The Cochrane review of 57 trials in 48,971 women found daily iron cut anaemia from 7.4 per cent to 4.0 per cent, and iron-deficiency anaemia at term from 18.4 per cent to 5.0 per cent. Nothing on this page argues against treating a deficiency.

Three questions that keep getting mixed up

Most arguments about iron in pregnancy happen because three different questions are being answered at the same time by people who think they are discussing one.

The first is whether to treat a woman who is already anaemic. The second is whether to give iron to a woman whose blood counts are fine, as a precaution. The third is whether any of it changes how the baby does. The evidence answers those three in three different tones of voice, and this page keeps them apart.

Question one: treating anaemia that is already there

Here the answer is settled and the argument has moved on to how. Tablets work. Iron given by vein works slightly faster, raising haemoglobin by about half a gram per decilitre more than tablets do three to six weeks in, across 11 trials in 2,935 women.

What that extra half gram buys is less clear than it sounds. In the Cochrane comparison the need for a blood transfusion was the same whichever route was used. In IVON, the largest trial of the question, a single infusion left 58 per cent of Nigerian women anaemic at 36 weeks against 61 per cent on tablets, which is no real difference. In Malawi a single infusion in the third trimester did much better, 46.7 per cent against 67.3 per cent, and still produced babies of the same weight.

Unsettled. Why the two African trials disagree is not resolved. The Malawi trial dosed later in pregnancy and compared against twice-daily tablets. IVON compared against three tablets a day in a setting with a lot of anaemia that is not caused by iron deficiency at all. When anaemia has another cause, no amount of iron fixes it, and that alone could explain the difference.

Pooling 15 trials of intravenous against oral iron, the outcomes that matter for the baby came out level: preterm birth, stillbirth and neonatal death were the same on both routes. The infusion is a convenience and adherence tool rather than a better drug.

The assumption underneath question one

Everything above assumes the anaemia being treated is made of iron shortage. Often it is not, and the trials that noticed tend to be the ones with null results.

Myth. Anaemia is a synonym for iron deficiency. In 310 young children in Puno, Peru, iron deficiency accounted for 27.5 per cent of the anaemia, inflammation for 45.9 per cent and other causes for the rest. In rural Cambodia, 340 anaemic women were randomised to an iron cooking ingot, to iron tablets or to neither, and after a year all three groups sat at 115 g/L. Only 9 per cent of them were short of iron at the start and inherited haemoglobin variants were common. Iron cannot fix an anaemia that was never about iron, and the trialists advise against the ingot wherever that pair of conditions holds.

That is the most likely reading of why IVON and the Malawi trial disagree, and it is the reason a ferritin result is worth more than a haemoglobin one before anybody starts treating.

Unsettled. The threshold that defines anaemia also moved. In 2024 WHO reviewed its haemoglobin cutoffs, changed the one for children aged 6 to 23 months and kept the one for the second trimester of pregnancy where it was, leaving the severity bands alone for want of evidence. Recalculated on the same blood samples in that Peruvian group, the share of children aged 6 to 23 months counted as anaemic fell from 62 to 47 per cent. The pregnancy cutoff survived that review, so the trials on this page still speak to the same population. A prevalence figure quoted without its cutoff no longer means much.

Question two: iron for women who are not anaemic

This is where guidelines disagree with each other, and the disagreement is honest, because the evidence supports two different readings of the same numbers.

Twenty-three studies in 4,492 non-anaemic pregnant women found that routine iron halves the risk of becoming anaemic later, with about ten women treated for each case prevented. In the same analysis birth weight, preterm birth and caesarean rates did not move at all.

Unsettled. So the honest summary is that preventive iron reliably protects a blood number and has not been shown to change how the birth goes. The authors of that review were blunt about the other half of the ledger too: reporting on harms was inconsistent, and there is not enough evidence to say what routine supplementation costs in stomach upset or iron overload.

That is why the US Preventive Services Task Force still says the evidence is insufficient to weigh the benefits and harms of routine screening and supplementation in pregnancy, while the World Health Organization recommends daily iron and folic acid for pregnant women. Both are reading the same trials. They differ on what to do when the benefit is certain and small and the harm is unmeasured.

Question three: does the baby benefit

A little, and less than the prevention story implies. Low birthweight fell from 6.1 per cent to 5.2 per cent across 12 trials in 18,290 infants, which works out at about ten babies in a thousand. Preterm birth did not move. Neonatal deaths and congenital anomalies did not move.

The bigger association people usually have in mind comes from observational data rather than from trials. Across 38 studies covering almost 32 million pregnancies, anaemia in pregnancy was linked to a 30 per cent higher chance of the baby growing poorly in the womb.

Myth. That association does not mean iron tablets prevent growth restriction. Anaemia travels with poverty, infection, malaria, poor diet and late antenatal care, and those things harm babies on their own. The trials that gave iron and watched what happened are the ones that answer the question, and they found small effects on birthweight and none on preterm birth.

The dosing question almost nobody is asked about

If you have taken iron tablets you already know the problem. Constipation, nausea, black stools, a metallic taste. It is the commonest reason women stop.

That impression holds up when it is counted. Pooling 43 trials of ferrous sulfate, the odds of gastrointestinal side effects ran at 2.32 against placebo, and in the seven of those trials done in pregnancy the odds were 3.33. The pregnancy figure carries a wide interval and the trials disagreed with each other, so take the direction from it and not the precision.

Established. Pooling 22 trials, taking iron intermittently instead of daily left haemoglobin slightly lower, by 0.24 g/dl, produced far fewer stomach side effects, with a relative risk of 0.27, and was taken more reliably, with adherence up by 60 per cent. The rate of anaemia came out the same either way.

That trade is worth putting plainly. A daily schedule that half the women abandon delivers less iron than an alternate-day schedule they stick to. If tablets are making you miserable, the conversation to have with your midwife is about the schedule rather than about giving up.

Unsettled. Outside pregnancy that comparison came out differently, and it is worth knowing before anyone treats alternate-day dosing as settled. Eleven trials in people with iron deficiency anaemia, with the pregnancy literature deliberately left out, counted side effects at the same rate on both schedules, a risk ratio of 1.07, and found haemoglobin 0.28 g/dL in favour of taking it daily. Certainty was rated very low throughout. The pregnancy case still rests on its own 22 trials. It travels less well than the absorption argument suggests.

What to do with this

If you are pregnant and have not been tested

Ask for the blood test, including ferritin rather than haemoglobin alone. Non-anaemic iron deficiency is common and invisible on a standard blood count, and the Lahore trial recruited 600 women who were exactly that. Requirements rise to 27 mg a day in pregnancy, which is more than most diets carry.

If your ferritin is low

Take the iron and expect it to work. Absorption from plant sources runs at roughly 5 to 12 per cent against 14 to 18 per cent on a mixed diet, and vitamin C in the same meal helps, so a citrus fruit or tomatoes next to the tablet is a free improvement. Tea, coffee and calcium at the same time work against it.

If the tablets are unbearable

Ask about alternate-day dosing before you stop. If you are anaemic and cannot absorb or tolerate tablets at all, intravenous iron is a reasonable alternative that raises haemoglobin a little faster, and the trials found no increase in serious harm.

Not for everyone. Do not take iron in pregnancy because it seems generally healthy. Iron you do not need is not cleared by the body, high-dose supplements commonly cause stomach upset, and the upper limit for adults is 45 mg a day. Iron tablets are also a leading cause of fatal poisoning in children under six, so where they are stored matters if there is a toddler in the house.

What would change this answer

• Nobody has run a large trial of screening with ferritin and treating only the women who are deficient. That is the design that would separate question one from question two, and until it exists the guideline disagreement stays reasonable.
• Harm reporting in the prevention trials is poor. The review that pooled them called explicitly for randomised trials quantifying gastrointestinal side effects and iron overload. Better harm data could move the balance either way.
• The two intravenous trials in Africa point in different directions, and the explanation probably lies in how much of the anaemia there is caused by something other than iron. Trials that measure the cause of anaemia before treating it would settle it.

How we searched

Sources

1. iron-p01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomised trials · n = 13,543 for this outcome, 48,971 across the review
   Iron supplementation during pregnancy may reduce maternal anaemia (4.0% versus 7.4%; risk ratio (RR) 0.30, 95% confidence interval (CI) 0.20 to 0.47; 14 trials, 13,543 women; low-certainty evidence)
   
   Who: pregnant women in 14 of the 57 trials for this outcome
   Effect: maternal anaemia 4.0 per cent against 7.4 per cent, risk ratio 0.30 (95% CI 0.20 to 0.47)
   Certainty: low-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
2. iron-p02 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 2,704
   probably reduces maternal iron-deficiency anaemia at term (5.0% versus 18.4%; RR 0.41, 95% CI 0.26 to 0.63; 7 trials, 2704 women; moderate-certainty evidence)
   
   Who: pregnant women, 7 trials
   Effect: iron-deficiency anaemia at term 5.0 per cent against 18.4 per cent, risk ratio 0.41 (95% CI 0.26 to 0.63)
   Certainty: moderate-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
3. iron-p03 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 14,060
   There is probably little to no difference in maternal death (2 versus 4 events, RR 0.57, 95% CI 0.12 to 2.69; 3 trials, 14,060 women; moderate-certainty evidence)
   
   Who: pregnant women, 3 trials
   Effect: maternal death 2 events against 4, risk ratio 0.57 (95% CI 0.12 to 2.69)
   Certainty: moderate-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
4. iron-p04 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 18,290
   Women taking iron supplements are probably less likely to have infants with low birthweight (5.2% versus 6.1%; RR 0.84, 95% CI 0.72 to 0.99; 12 trials, 18,290 infants; moderate-certainty evidence)
   
   Who: infants in 12 trials
   Effect: low birthweight 5.2 per cent against 6.1 per cent, risk ratio 0.84 (95% CI 0.72 to 0.99)
   Certainty: moderate-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
5. iron-p05 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 18,827
   There is probably little to no difference in preterm birth (7.6% versus 8.2%; RR 0.93, 95% CI 0.84 to 1.02; 11 trials, 18,827 infants; moderate-certainty evidence)
   
   Who: infants in 11 trials
   Effect: preterm birth 7.6 per cent against 8.2 per cent, risk ratio 0.93 (95% CI 0.84 to 1.02)
   Certainty: moderate-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
6. iron-p06 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 2,423
   The evidence is very uncertain for adverse effects (21.6% versus 18.0%; RR 1.29, 95% CI 0.83 to 2.02; 12 trials, 2423 women; very low-certainty evidence)
   
   Who: pregnant women, 12 trials
   Effect: adverse effects 21.6 per cent against 18.0 per cent, risk ratio 1.29 (95% CI 0.83 to 2.02)
   Certainty: very low-certainty evidence
   Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
7. iron-p07 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised and observational studies · n = 4,492
   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.
   
   Who: non-anaemic pregnant women, 23 studies
   Effect: anaemia relative risk 0.50 (95% CI 0.34 to 0.74), number needed to treat 10; no difference in birth weight, preterm birth or caesarean rate
   Certainty: high certainty for the anaemia outcome, moderate for haemoglobin and ferritin
   Ng et al., Family Practice, 2025 · checked 2026-09-16 · we read the abstract
8. iron-p08 · Meta-analysis or systematic review · systematic review and meta-analysis of trials · n = 22 trials
   Intermittent regimens had lower gastric side effects (relative risk (RR), 0.27; 95%CI, 0.11, 0.69) and better medication adherences (relative risk (RR), 1.6; 95%CI, 1.34, 1.91). There was no clear evidence of a difference in anaemia incidence between the groups (relative risk (RR), 1.09; 95%CI, 0.77, 1.54).
   
   Who: pregnant women in low and middle income countries, 22 trials
   Effect: haemoglobin mean difference -0.24 g/dl; gastric side effects relative risk 0.27 (95% CI 0.11 to 0.69); adherence relative risk 1.6 (95% CI 1.34 to 1.91); anaemia incidence relative risk 1.09 (95% CI 0.77 to 1.54)
   Certainty: evidence ranges from high to very low
   Tamiru et al., Reproductive Health, 2025 · checked 2026-09-16 · we read the abstract
9. iron-p09 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomised trials · n = 3,939
   Compared with oral iron, intravenous iron likely slightly increases Hb level three to six weeks after treatment start (MD 0.49, 95% CI 0.28 to 0.69; 11 RCTs; 2935 participants; moderate-certainty evidence)
   
   Who: pregnant women with confirmed iron deficiency anaemia, mostly in India and Africa, 13 trials
   Effect: haemoglobin mean difference 0.49 g/dL at three to six weeks (95% CI 0.28 to 0.69), 11 trials and 2,935 participants; anaemia status 0.81 (95% CI 0.77 to 0.86), 5 trials and 2,189 participants
   Certainty: moderate-certainty evidence
   Bhandari et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
10. iron-p10 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = 2,592
    likely results in little to no difference in the need for blood transfusion (RR 0.97, 95% CI 0.58 to 1.60; 6 RCTs; 2592 participants; moderate-certainty evidence)
    
    Who: pregnant women with iron deficiency anaemia, 6 trials
    Effect: need for blood transfusion risk ratio 0.97 (95% CI 0.58 to 1.60)
    Certainty: moderate-certainty evidence
    Bhandari et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · we read the abstract
11. iron-p11 · Randomised controlled trial(s) · multicentre, open-label randomised controlled trial · n = 1,056
    No significant difference was found in anaemia at 36 weeks (299 [58%] of 517 in the intravenous group vs 305 [61%] of 503 in the oral group; risk ratio 0.95, 95% CI 0.85-1.06; p=0.36), nor in preterm birth (73 [14%] of 518 vs 77 [15%] of 513; 0.94, 0.70-1.26; p=0.66).
    
    Who: pregnant women with haemoglobin below 10 g/dL at 20 to 32 weeks, 11 facilities in Lagos and Kano
    Effect: anaemia at 36 weeks 58 per cent against 61 per cent, risk ratio 0.95 (95% CI 0.85 to 1.06); preterm birth risk ratio 0.94 (95% CI 0.70 to 1.26)
    Certainty: large pragmatic trial, open label
    Afolabi et al., The Lancet Global Health, 2024 · checked 2026-09-16 · we read the abstract
12. iron-p12 · Randomised controlled trial(s) · open-label, individually randomised controlled trial · n = 590
    At the primary timepoint, 126 of 270 (46.7%) of women in the FCM group were anemic, compared to 170 of 271 (67.3%) women in the standard-of-care group (PR, 0.74 (95% CI 0.64, 0.87); P = 0.0002). There was no difference between groups in birthweight (mean difference 10.9 g (-65.7, 87.5 g); P = 0.78).
    
    Who: women at 27 to 35 weeks with capillary haemoglobin below 10.0 g/dL, southern Malawi
    Effect: anaemia 46.7 per cent against 67.3 per cent, prevalence ratio 0.74 (95% CI 0.64 to 0.87); birthweight mean difference 10.9 g (95% CI -65.7 to 87.5)
    Certainty: single trial with clear primary outcomes
    Pasricha et al., Nature Medicine, 2025 · checked 2026-09-16 · we read the abstract
13. iron-p13 · Randomised controlled trial(s) · multicentre, two-arm randomised controlled trial · n = 600
    Maternal haemoglobin concentration before delivery was 11·6 g/dL (SD 0·5) in the intravenous iron group and 10·8 g/dL (0·7) in the prophylactic oral iron group (mean difference, 0·74 g/dL [95% CI 0·64-0·85]; p<0·0001).
    
    Who: pregnant women with haemoglobin 11 to 13 g/dL and ferritin below 30 micrograms per litre, three hospitals in Lahore
    Effect: haemoglobin before delivery 11.6 against 10.8 g/dL, mean difference 0.74 g/dL (95% CI 0.64 to 0.85)
    Certainty: single trial, haemoglobin rather than a clinical outcome
    Mehmood et al., The Lancet Haematology, 2026 · checked 2026-09-16 · we read the abstract
14. iron-p14 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials · n = 8,431 for preterm birth
    Seven studies with 8431 pregnancies analyzed the risk of preterm birth, and the risk appeared to be similar in both groups (RR 0.96, CI 0.86 to 1.07; moderate certainty evidence).
    
    Who: pregnancies in 7 trials for preterm birth, 5 for stillbirth
    Effect: preterm birth risk ratio 0.96 (95% CI 0.86 to 1.07) in 7 studies and 8,431 pregnancies; stillbirth 0.85 (0.64 to 1.13) in 5 studies and 8,639 pregnancies; neonatal mortality 2.0 per cent against 2.3 per cent
    Certainty: moderate certainty for preterm birth, low for the rest
    Tuomi et al., European Journal of Pediatrics, 2025 · checked 2026-09-16 · we read the abstract
15. iron-p15 · Observational data · systematic review and meta-analysis of observational studies · n = 31,850,299
    The pooled analysis demonstrated that anaemia in pregnancy is associated with a significantly increased risk of IUGR (OR = 1.30, 95% CI: 1.05-1.62, I² = 97%).
    
    Who: 3,871,849 anaemic and 27,978,450 non-anaemic pregnant women, 38 studies
    Effect: intrauterine growth restriction odds ratio 1.30 (95% CI 1.05 to 1.62), heterogeneity 97 per cent
    Certainty: observational data only, very high heterogeneity, subgroup results not significant
    Alsharif et al., Maternal & Child Nutrition, 2025 · checked 2026-09-16 · we read the abstract
16. iron-02 · Position of an expert body
    Men 19+: 8 mg; Women 19–50: 18 mg; Women 51+: 8 mg; Pregnancy: 27 mg
    
    Who: adults
    Effect: 8 / 18 / 8 / 27 mg per day
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
17. iron-03 · Position of an expert body
    The requirement for iron is 1.8 times higher for people who follow vegetarian diets than those for people who include animal products in their diet.
    
    Who: vegetarians
    Effect: ×1.8 requirement
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
18. iron-04 · Position of an expert body
    The bioavailability of iron is approximately 14% to 18% from mixed diets that include substantial amounts of meat, seafood, and vitamin C (ascorbic acid, which enhances the bioavailability of nonheme iron) and 5% to 12% from vegetarian diets.
    
    Who: adults
    Effect: 14–18% vs 5–12% absorption
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
19. iron-05 · Position of an expert body
    In addition to ascorbic acid, meat, poultry, and seafood can enhance nonheme iron absorption, whereas phytate (which is present in grains and beans) and certain polyphenols in some nonanimal foods (e.g., cereals, legumes) have the opposite effect.
    
    Who: general
    Effect: enhancers and inhibitors of non-heme iron
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
20. iron-06 · Position of an expert body
    Unlike other inhibitors of iron absorption, calcium might reduce the bioavailability of both nonheme and heme iron.
    
    Who: general
    Effect: reduced absorption of both forms
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
21. iron-07 · Position of an expert body
    The functional deficits that are associated with IDA include gastrointestinal disturbances; weakness; fatigue; difficulty concentrating; and impaired cognitive function, immune function, exercise or work performance, and body temperature regulation.
    
    Who: people with iron deficiency anaemia
    Effect: functional deficits
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
22. iron-09 · Position of an expert body
    The ULs apply to healthy infants, children, and adults with a limit of 45 mg for adults ages 14–50+.
    
    Who: adults 14+
    Effect: UL 45 mg/day
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
23. iron-10 · Position of an expert body
    High-dose iron supplements can also cause gastrointestinal effects, including gastric upset, constipation, nausea, abdominal pain, vomiting, and diarrhea.
    
    Who: people taking high-dose iron
    Effect: gastrointestinal side effects
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
24. iron-17 · Meta-analysis or systematic review
    the U.S. Preventive Services Task Force (USPSTF) has concluded that the current evidence is insufficient to assess the balance of benefits and harms of both screening for iron deficiency and IDA in pregnant women and routinely supplementing them with iron
    
    Who: pregnant women
    Effect: insufficient evidence for routine screening or supplementation
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15
25. iron-18 · Position of an expert body
    Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron. Heme iron has higher bioavailability than nonheme iron, and other dietary components have less effect on the bioavailability of heme than nonheme iron.
    
    Who: general
    Effect: bioavailability, direction: lower from plant sources
    NIH Office of Dietary Supplements, Iron - Health Professional Fact Sheet · checked 2026-09-16
26. iron-r2-7 · Meta-analysis or systematic review · meta-regression within a systematic review and meta-analysis of randomised trials, testing the study odds ratio against iron dose · n = 6,831 participants overall; 1,028 in the pregnancy subgroup
    Likewise, subgroup analysis of pooled data from 7 RCTs in pregnant women (n = 1028) showed a statistically significant increased risk of GI side-effects for ferrous sulfate although there was marked heterogeneity in the data (OR = 3.33, 95% CI 1.19-9.28, p = 0.02, I2 = 66.1%). Meta-regression did not provide significant evidence of an association between the study OR and the iron dose.
    
    Who: adults in 43 randomised trials of ferrous sulfate, including a subgroup of 7 trials in pregnant women
    Effect: meta-regression found no significant association between the study odds ratio and the iron dose; in pregnant women the odds ratio for gastrointestinal side effects was 3.33 (95% CI 1.19 to 9.28)
    Certainty: absence of an association is not proof there is none: doses across trials clustered in a narrow therapeutic range, and the pregnancy subgroup was markedly heterogeneous (I2 66 per cent) with a very wide confidence interval
    Tolkien et al., PLoS One, 2015 · checked 2026-09-17 · we read the abstract
27. iron-r3-06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised controlled trials comparing daily with alternate-day oral iron · n = 1,014 participants
    The pooled analysis found a small, statistically non-significant increase in hemoglobin with daily dosing over alternate-day (MD: 0.28, 95% CI: -0.01 to 0.56, p = 0.06, z = 1.91). Secondary outcomes revealed no significant differences among groups for serum iron, ferritin, transferrin saturation, TIBC, and MCV. Adverse effects were similar between groups (RR: 1.07, 95% CI: 0.86 to 1.34), though metallic taste was more frequent with daily dosing.
    
    Who: people with iron deficiency anaemia in the general population, excluding the pregnancy-specific literature; 11 randomised trials
    Effect: haemoglobin mean difference 0.28 in favour of daily dosing (95% CI -0.01 to 0.56, p = 0.06), adverse events risk ratio 1.07 (95% CI 0.86 to 1.34)
    Certainty: certainty of evidence rated very low for most outcomes because of heterogeneity and imprecision; the confidence interval crosses no difference
    BMC Pharmacology and Toxicology, 2025 · checked 2026-09-17 · we read the abstract
28. iron-e1-05 · Randomised controlled trial(s) · randomised controlled trial with three arms over 12 months, blood at baseline, 6 and 12 months · n = 340 women randomised to iron ingot, 18 mg/day iron supplement, or non-placebo control
    Neither the iron ingot nor iron supplements increased hemoglobin concentrations in this population at 6 or 12 mo.
    
    Who: 340 rural Cambodian women aged 18-49 with mild or moderate anaemia; at baseline only 9% were iron deficient by ferritin, and structural haemoglobin variants were common
    Effect: mean haemoglobin at 12 months 115 g/L in all three arms; ferritin was higher in the supplement arm at 6 months (P = 0.002) but not at 12 months
    Certainty: this is the crucial detail and the page must carry it: the anaemia in this population was mostly not from iron shortage, so a null result here is about who was treated, not proof that iron ingots never work. The registered primary endpoint, haemoglobin at 12 months (NCT02341586), matches what was reported. Full text not available to us (not in PMC)
    Rappaport et al., American Journal of Clinical Nutrition, 2017 · checked 2026-09-18 · we read the abstract
29. iron-e1-06 · Randomised controlled trial(s) · randomised controlled trial, authors' conclusion · n = 340 women
    We do not recommend the use of the fish-shaped iron ingot in Cambodia or in countries where the prevalence of iron deficiency is low and genetic hemoglobin disorders are high.
    
    Who: rural Cambodian women with anaemia largely unrelated to iron
    Effect: the authors advise against the fish-shaped iron ingot in Cambodia and in countries where iron deficiency prevalence is low and genetic haemoglobin disorders are high
    Certainty: a recommendation from one trial in one province; it is quoted because the marketing of this device made no such distinction, and the distinction is the whole finding. Full text not available to us (not in PMC)
    Rappaport et al., American Journal of Clinical Nutrition, 2017 · checked 2026-09-18 · we read the abstract
30. iron-e1-12 · Position of an expert body · WHO guideline with systematic evidence review and a guideline development group · n = normative guidance, not a study
    Analysis of the evidence suggested modification of the current haemoglobin cutoffs for defining anaemia for one population group (children 6–23 months of age) and use of the existing cutoff for pregnant women in the second trimester.
    
    Who: all population groups for whom WHO sets haemoglobin cutoffs
    Effect: the evidence supported changing the haemoglobin cutoff for children aged 6-23 months and keeping the existing cutoff for women in the second trimester of pregnancy; severity bands were left as they were for lack of evidence, with severe anaemia retained at under 70 g/L for those two groups
    Certainty: a normative decision, not a measurement; it changes who counts as anaemic without changing anyone blood
    WHO, Guideline on haemoglobin cutoffs to define anaemia in individuals and populations, 2024 · checked 2026-09-18 · we read the section
31. iron-e1-13 · Observational data · cross-sectional study recalculating anaemia prevalence under the old and the new WHO cutoffs in the same blood samples · n = 310 children
    Applying the new WHO guidelines, anemia prevalence changed from 50% to 42.2% in children aged 6-59 months (62% to 47% in children aged 6-23 months and from 45.9% to 40.6% in children aged 24-59 months).
    
    Who: 310 children aged 6-59 months in Puno, Peru, recruited by convenience sampling at routine check-ups
    Effect: prevalence fell from 50% to 42.2% overall, from 62% to 47% in children aged 6-23 months and from 45.9% to 40.6% in those aged 24-59 months
    Certainty: convenience sampling in one high-altitude region, so the size of the shift is local; the direction is a property of the new cutoffs and altitude adjustment, not of Peru
    PLoS ONE, 2026 · checked 2026-09-18 · we read the abstract
32. iron-e1-14 · Observational data · cross-sectional study with serum biomarkers and adjusted Poisson regression · n = 310 children
    The proportion of anemia due to ID was 27.5%, due to inflammation was 45.9%, and due to other causes was 26.6%.
    
    Who: 310 children aged 6-59 months in Puno, Peru
    Effect: 27.5% of anaemia attributed to iron deficiency (ferritin under 12 ng/mL), 45.9% to inflammation (IL-6 above 60 pg/mL) and 26.6% to other causes
    Certainty: a single high-altitude setting with high infection burden, and the attribution depends entirely on the cutoffs chosen for ferritin and IL-6; it is recorded because iron pages routinely treat anaemia and iron deficiency as the same thing, and the iron-fish trial failed for exactly this reason
    PLoS ONE, 2026 · checked 2026-09-18 · we read the abstract