Prospective association of metal levels with gestational diabetes mellitus and glucose: A retrospective cohort study from South China.

OBJECTIVE: To explore the prospective correlation between serum metals before 24 weeks' gestation and gestational diabetes mellitus (GDM) or glucose in the late second trimester among southern Chinese pregnant women. METHODS: A total of 8169 pregnant women were included in our retrospective cohort study. Logistic regression was used to investigate the relationships between metals (Manganese [Mn], copper [Cu], lead [Pb], calcium [Ca], zinc [Zn], magnesium [Mg]) and GDM. Quantile regression was performed to detect the shifts and associations with metals and three time-points glucose distribution of oral glucose tolerance test (OGTT) focused on the 10th, 50th, and 90th percentiles. Weighted quantile sum (WQS) regression was used to explore the relationship of metal mixtures and GDM as well as glucose. RESULTS: Maternal serum concentrations of metals were assessed at mean 16.55 ± 2.92 weeks' gestation. Women with under weight might have 25% decreased risk of GDM for every 50% increase in Cu concentration within the safe limits. A 50% increase in Mn and Zn levels was related to a 0.051 µmol/L (95% CI: 0.033-0.070) and 0.059 µmol/L (95% CI: 0.040-0.079) increase in mean fasting plasma glucose of OGTT (OGTT0), respectively. The magnitude of association with Mn was smaller at the upper tail of OGTT0 distribution, while the magnitude of correlation with Zn was greater at the upper tail. However, there was a 0.012 mmol/L (95% CI: -0.017 to -0.008), 0.028 mmol/L (95% CI: -0.049 to -0.007), and 0.036 mmol/L (95% CI: -0.057 to -0.016) decrease in mean OGTT0 levels for every 50% increase in Pb, Ca, and Mg, respectively. The negative association of Pb, Ca, and Mg was greater at the lower tail of OGTT0 distribution. No significant relationship was observed in Cu and mean OGTT0 level (-0.010 mmol/L, 95% CI: -0.021 to 0.001), however, it showed a protective effect at the upper tail (-0.034 mmol/L, 95% CI: -0.049 to -0.017). No obvious correlation was found between metals and postprandial glucose levels (OGTT1 and OGTT2 from OGTT). The WQS index was significantly related to OGTT0 (P < 0.001). The contribution of Mn (80.19%) to metal mixture index was the highest related to OGTT0, followed by Cu (19.81%). CONCLUSIONS: Higher Mn and Zn but lower Pb, Ca, and Mg concentrations within a certain range before 24 weeks' gestation might prospectively impair fasting plasma glucose during pregnancy; a greater focus is required on Mn. It could provide early markers of metal for predicting later glucose and suggest implement intervention for pregnant women.