Association of iron status during early pregnancy and the risk of gestational diabetes: a retrospective cohort study in Shanghai.

BACKGROUND

The association between maternal iron status and the risk of gestational diabetes mellitus (GDM) remains elusive. Clearer evidence is needed to inform appropriate ferritin thresholds and iron supplementation guidelines during pregnancy.

OBJECTIVES

To investigate whether first-trimester serum ferritin (SF) concentration is associated with subsequent GDM risk.

DESIGN

Retrospective cohort study.

SETTING

A tertiary obstetrics and gynaecology hospital in Shanghai, China.

PARTICIPANTS

A total of 6429 low-risk pregnant women at fewer than 14 weeks of gestation were finally included.

OUTCOME MEASURES: GDM was diagnosed using a 75 g oral glucose tolerance test according to the criteria established by the International Association of Diabetes and Pregnancy Study Groups (IADPSG). Women were stratified by SF concentration into three groups: <30, 30-70 and >70 µg/L. Logistic regression was used to calculate adjusted ORs and 95% CIs for GDM, with the 30-70 µg/L group serving as the reference.

RESULTS

GDM was diagnosed in 1215 women (18.9%). Elevated SF (>70 µg/L) was independently associated with increased GDM risk (adjusted OR 1.27, 95% CI 1.05 to 1.54) compared with the reference group (30-70 µg/L). Stratified analysis revealed that the association was significant only in normal-weight women (body mass index (BMI)<24 kg/m²; OR 1.46, 95% CI 1.19 to 1.79), while no significant association was observed in overweight or obese women, indicating effect modification by prepregnancy BMI.

CONCLUSIONS

Elevated first-trimester SF is independently associated with GDM risk in pregnant women at low-risk, with the association most pronounced among those with normal prepregnancy BMI.