TABLE 1.

Evidence map for adverse health outcomes associated with high SF concentration, high hemoglobin concentration, high iron intake, or iron supplementation in pregnant women and young children¹

	Study type
		Observational			RCT
Health outcome	Mechanistic: in vitro	Retrospective	Case control2	Prospective	Primary	Secondary	Nature of evidence based on iron exposure indicator
GDM/T2D-PP3	—4		√	√	√	√	Supplementation: inconsistent5 SF concentration: consistent;6 intake: inconsistent
Preterm birth7		√	√	√			Hemoglobin concentration: inconsistent across trimesters SF concentration; consistent
Impaired fetal growth8		√	√	√			Supplementation: consistent; hemoglobin concentration: inconsistent across trimesters SF concentration: inconsistent
Impaired infant/child growth9					√		Supplementation to iron replete: consistent
Long-term impaired cognitive development10						√	Supplementation to iron replete: limited
Diarrhea11					√	√	Supplementation or fortification: inconsistent
Intermediate outcome
Microbiome change12	√				√	√	Supplementation: inconsistent

¹A check (√) indicates available evidence for each study type. GDM, gestational diabetes mellitus; RCT, randomized controlled trial; SF, serum ferritin; T2D-PP, type 2 diabetes postpartum.

²Includes nested studies.

³From references 39–48.

⁴Only one animal study (rats) on high-fructose diet induced GDM; there was no additional effect on GDM with a moderate 83% increase in dietary iron (49).

⁵Inconsistent indicates discordant results. In this case, discordant results for supplemental iron and GDM from observational studies and RCT.

⁶Consistent indicates concordant results. In this case, concordant results reported associating SF with GDM risk from observational studies.

⁷From references 33, 50–53.

⁸From references 33, 51, 54.

⁹From references 55–60.

¹⁰From reference 61.

¹¹From reference 62.

¹²From references 63–66.