Reviews/Iron Status/Intravenous iron reduces low birthweight
Preg · IRON-PREG-02 · v2
The question is whether giving iron by vein rather than by mouth lowers the chance of a baby being born too small. The one large trial designed to answer this found fewer low-birthweight babies with one intravenous formulation, ferric carboxymaltose, but not with a second intravenous formulation, ferric derisomaltose, given in the same study [3]. Two other large trials of ferric carboxymaltose found no difference in birthweight at all [2][4], and a smaller trial of a different intravenous iron found babies were slightly heavier but not by a reliable margin [7]. Because the benefit shows up for only one formulation in only one trial and is missing everywhere else, the panel judged that the broad statement claims more than the evidence supports. A single favourable result cannot outweigh the trials that found nothing.
Only one trial in the corpus was designed with low birthweight as a primary outcome, and it found a reduced rate with intravenous ferric carboxymaltose (25.2%, relative risk 0.87, P=.017) but not with intravenous ferric derisomaltose (29.1%, relative risk 0.98, P=.71) versus oral iron (29.3%) [3]. Two large ferric carboxymaltose trials reported no birthweight difference (mean difference 10.9 g, P=0.78 [2]; mean difference -3.1 g, P=0.93 [4]). A ferumoxytol trial reported a larger but non-significant birthweight (3215 g vs 3033 g, P=.09) [7]. A small comparative study reported birthweight was better in the intravenous group but gave no effect size [5], while [1] is a protocol and [6] reports no birthweight result. The corpus is inconsistent and the one positive result is formulation-specific. The contested point: The division is whether a class-level effect exists: the single positive arm in [3] sits against the null second intravenous arm in the same trial and two large null trials [2][4]. Compounding this, [3] measured the dichotomous low-birthweight rate while [2] and [4] measured continuous birthweight, so the trials do not cleanly measure the same endpoint.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
The blanket claim rests on a single arm of a single trial: in [3] FCM reduced LBW but the co-randomised ferric derisomaltose arm showed no effect (RR 0.98, P=.71), so 'intravenous iron' as a class does not reduce LBW.
The two other large FCM RCTs ([2] MD 10.9 g P=0.78; [4] MD -3.1 g P=0.93) are null on birthweight, directly contradicting the positive result in [3].
Where it remains uncertain. Two large ferric carboxymaltose trials found no birthweight difference (mean difference 10.9 g, P=0.78 [2]; mean difference -3.1 g, P=0.93 [4]), contradicting the single positive result.
Aleatory
The single significant result has an upper confidence bound of 0.99 and P=.017 against a prespecified alpha of 0.0245 [3], leaving little margin against random variation.
The load-bearing papers from a corpus of 11, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Large FCM-vs-oral RCT with birthweight as a primary outcome shows no benefit, contradicting the claim.
“There was no difference between groups in birthweight (mean difference 10.9 g (-65.7, 87.5 g); P = 0.78).”
Panel auditInternal validity: high · scope of inference: Third-trimester (27-35 weeks) anaemic women in southern Malawi with capillary Hb <10 g/dl.Key limitations: open-label · continuous birthweight not LBW dichotomy · late-pregnancy enrolment
Only trial with LBW as a primary outcome; supports the claim for FCM but refutes it for derisomaltose within the same trial.
“There was a reduced rate of low birth weight with intravenous ferric carboxymaltose (25·2%, relative risk 0·87 [97·55% confidence interval 0.75, 0.99], P=.017), but not intravenous ferric derisomaltose (29.1%, relative risk 0.98 [97.55% confidence interval 0.86, 1.12], P=.71) vs oral iron (29.3%).”
Panel auditInternal validity: high · scope of inference: Singleton pregnancies with moderate iron deficiency anaemia (Hb 7.0-9.9) treated at 14-17 weeks across 4 sites in India.Key limitations: semiblind (open) design · effect confined to the FCM formulation, not derisomaltose · second-trimester moderate IDA only
Second large FCM-vs-oral RCT with birthweight as a primary neonatal outcome shows no benefit.
“Birthweight did not differ between groups (mean difference -3·1 g [-75·0 to 68·9, p=0·93).”
Panel auditInternal validity: high · scope of inference: Singleton pregnancies at 13-26 weeks with capillary Hb <10 g/dl and negative malaria test in malaria-endemic southern Malawi.Key limitations: open-label for participants and nurses · continuous birthweight not LBW dichotomy · malaria-endemic setting
It states a hypothesis that LBW will be lower in the intravenous arms but reports no outcome data.
Panel auditInternal validity: not assessable from abstract · scope of inference: Design intent for moderate iron deficiency anaemia in pregnant Indian women treated in the second trimester; no findings.Key limitations: protocol only, no results · no sample size in abstract
4 of 11 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
A single borderline positive arm cannot carry a general claim against two large null trials and a null second IV formulation.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Replication of the ferric carboxymaltose low-birthweight effect. The reduction rests on a single trial [3] with a borderline confidence bound and is contradicted by continuous-birthweight nulls in [2] and [4]. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: An independent trial powered on the dichotomous low-birthweight rate with ferric carboxymaltose versus oral iron.
Open question: Does intravenous ferric carboxymaltose reduce the low-birthweight rate in a second, independent trial? Why it is still open: The only positive low-birthweight result comes from a single trial [3] with an upper confidence bound at 0.99, and is not reproduced by [2] or [4].
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 18 Sep 2026 · protocol v0.19