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

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<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.

Higher dietary vitamin C intake is associated with a lower risk of gestational diabetes mellitus: A longitudinal cohort study.

BACKGROUND & AIMS: Oxidative stress has been implicated in the pathogenesis of gestational diabetes mellitus (GDM). Vitamin C as natural antioxidant may help to increase the body's antioxidant capacity. The study is aimed to determine whether vitamin C intake during pregnancy is associated with lower risk of GDM. METHODS: Women with singleton pregnancy and without any history of diabetes were drawn from the ongoing Tongji Maternal and Child Health Cohort (TMCHC). Oral glucose tolerance tests (OGTT) were conducted during weeks 24-28 of gestation to screen for GDM. A validated food frequency questionnaire (FFQ) was used to assess dietary intake during mid pregnancy. Use of multivitamins and specific supplements of vitamin C was assessed by questionnaires. Odds ratios (ORs) of GDM risk were calculated by logistic regression models, adjusted for potential confounders. RESULTS: 344 (11.4%) of the 3009 women were diagnosed with GDM. Dietary vitamin C intake was inversely associated with the risk of GDM. Women with above adequate dietary vitamin C intake (more than 200 mg/day) experienced lower odds of GDM (OR 0.68, 95% CI: 0.49-0.95) than those with adequate intake (115-200 mg/day). There was no association between the total consumption of vitamin C and the risk of GDM (OR 1.04, 95% CI: 0.71-1.53). CONCLUSION: This data suggests that higher dietary consumption of vitamin C during pregnancy is independently associated with lower odds of GDM. Above 200 mg/day of dietary vitamin C intake may help reduce the odds of GDM. However, no such association between total vitamin C intake and the risk of GDM was found. Hence, sufficient vegetables and fruits rich in vitamin C should be recommended to protect pregnant women from developing gestational diabetes.