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OBJECTIVES: Concerns relative to excessive iron intake are raised when high iron status exposure has been linked in observational studies to a greater risk of gestational diabetes mellitus (GDM). We aimed to examine the association between iron intake during pregnancy and GDM risk in Chinese women. METHODS: The study included 2174 pregnant women from the Tongji Maternal and Child Health Cohort (TMCHC), a prospective cohort in Wuhan, China. Iron intakes from food and supplementation prior to GDM diagnosis were assessed using a validated food frequency questionnaire (FFQ) and a detailed supplement questionnaire collected at 13–28 weeks of gestation. GDM was ascertained by an oral glucose tolerance test at 24–28 weeks of gestation. Odd ratios (ORs) of GDM in relation to categories of iron intake (i.e., quartiles of total and food iron intake, categories of supplemental iron intake [0, 0–30, >30 mg/day]) were estimated using logistic regression models, with adjustment for demographic, dietary and lifestyle factors. RESULTS: A total of 242 (11.1%) women were diagnosed with GDM. The adjusted ORs (95% CIs) for the risk of GDM associated with the higher quartiles compared with the lowest quartile of total iron intake were 1.44 (0.89, 2.33), 2.03 (1.27, 3.25), and 2.86 (1.84, 4.43), respectively (P for trend 30 mg/day during pregnancy had an OR for GDM of 2.32 (95% CI: 1.60, 3.36). Moreover, the significant positive effect of supplemental iron was mainly attributed to iron supplementation during mid-pregnancy (≥60 vs. 0 mg/day, OR: 1.46, 95% CI: 1.00, 2.13), while no effect of iron supplementation during early pregnancy was observed. No significant association was found between food iron intake and GDM. CONCLUSIONS: Higher supplemental iron intake during pregnancy was significantly associated with elevated GDM risk. Adverse effect of indiscriminate iron supplementation, especially inappropriate supplementation during mid-pregnancy, would likely outweigh benefits for maternal health. FUNDING SOURCES: Funding was received from the National Natural Science Foundation of China (NSFC81673159), National Program on Basic Research Project of China (NO.2013FY114200) and the Fundamental Research Funds for the Central Universities (HUST 2019kfyXMPY008) (Nianhong.Yang.).

OBJECTIVES: The overall plant-based diet index (PDI) has been demonstrated to be protective against type 2 diabetes (T2D) in the general population. Whether the PDI was linked to gestational diabetes mellitus (GDM) is unclear. We aimed to assess the association of the PDI with GDM incidence in Chinese pregnant women. METHODS: A total of 2099 pregnant women from the Tongji Maternal and Child Health Cohort (TMCHC) were included in the present study. Dietary data were collected at 13–28 wks of pregnancy by using a validated semi-quantitative food frequency questionnaire (FFQ). Food groups including cereals, fruits, vegetables, nuts, beans, vegetable oil, dairy, eggs, meat, and fish, were ranked into quintiles and given positive (1–5 for plant food groups) or reverse (5–1 for animal food groups) scores. The PDI was obtained by summing the 10 food group scores, with a theoretical range of 10 to 50. GDM was diagnosed by the 75-g 2-h oral glucose tolerance test at 24–28 wks. Cubic-restricted spline function and logistic regression analyses were used to examine the association between the PDI during pregnancy and GDM. RESULTS: GDM was reported by 8.1% of the 2099 pregnancies. The PDI score ranged from 17 to 43 (theoretical range: 10–50), the mean (SD) was 30.2 (4.4). After adjusting for maternal age, ethnicity, education, income, parity, gravidity, family history of diabetes, total energy intake per day, and other pre-pregnancy information such as body mass index (BMI), smoking status, drinking status, exercise, and sleep quality, a linear association between the PDI and GDM risk was demonstrated by the restricted cubic splines (P for overall association = 0.024, P for nonlinearity = 0.370). Compared to the lowest quartile 1 of PDI, ORs (95% CI) were 0.91 (0.59, 1.42) for quartile 2, 0.91 (0.58, 1.41) for quartile 3, and 0.52 (0.30, 0.89) for quartiles 4 (P for trend = 0.040) in the adjusted model. CONCLUSIONS: Our study suggests that higher PDI is associated with a substantially lower risk of developing GDM, which indicates that adopt plant-based diets during pregnancy could be an easy avenue to reduce GDM risk. FUNDING SOURCES: Funding was received from the National Program on Basic Research Project of China (NO.2013FY114200) and the Fundamental Research Funds for the Central Universities (HUST2016YXZD040) for Nianhong Yang.