Periconceptional iron supplementation and risk of gestational diabetes mellitus: a prospective cohort study.

Abstract Aims Iron supplementation has been recommended for healthy pregnancy, but concerns have been raised regarding the potential adverse effects. We sought to examine the impact of periconceptional iron supplement use on subsequent gestational diabetes mellitus (GDM) risk. Methods Participants (N=5101) with information on periconceptional micronutrient supplementation and diagnosis of GDM were involved. Information on iron supplementation and general characteristics were collected at enrollment and follow-up visits. GDM was diagnosed by oral glucose tolerance tests (OGTT) conducted at 24-28 weeks of gestation. Robust Poisson regression model was used to estimate the relative risks (RRs) and 95% confidence intervals (CI) for the effect of iron supplement use on GDM. Results 10.5% of the participants were diagnosed with GDM and the incidence was significantly higher in users with iron >30 mg/d for more than 3 months (Iron>30-L) than in nonusers. Adjusted RRs (95% CI) were 1.53 (1.21, 1.93) in Iron>30-L group, 1.14 (0.80, 1.61) in users with iron >30 mg/d for less than 3 months (Iron>30-S) and 1.15 (0.86, 1.54) in users with iron ≤30 mg/d for any duration (Iron≤30) respectively, compared to nonusers. This link in Iron>30-L group was even stronger (adjusted RR: 1.70, 95% CI: 1.25, 2.31) when restricting the analysis among primiparous and iron-replete participants without family history of diabetes. There were no significant differences in birth outcomes among groups. Conclusions Periconceptional iron supplementation>30 mg/d for long-term was associated with increased GDM risk. The need and safety of prophylactic iron supplement in iron-replete pregnant women should be reconsidered.