Nobody can say whether routine iron in pregnancy does any harm
Twenty-three studies of iron in non-anaemic pregnant women reported harms too inconsistently to tell. That is an absence of evidence, not a finding of safety.
What the study found
Whether routine iron in pregnancy harms anyone was never measured
Twenty-three studies of iron in non-anaemic pregnant women reported harms so inconsistently that the reviewers could not tell whether supplementation causes any negative outcome at all. That is an absence of evidence, not a finding of safety.
The caveat · Routine use only, not treatment
This concerns routine supplementation in women who are not anaemic, not the treatment of a diagnosed deficiency, where the case is different. The reviewers name the practical consequence themselves: international guidelines on this point disagree with each other. The same review mixes randomised trials with observational studies.