TPO and hyperinsulinemic hypoglycemia, familial, 4: Wu et al. found that Fe and Mg levels in pregnant women were negatively correlated with TSH levels and positively correlated with FT3 levels, FT4 levels, and the FT3/FT4 ratio, and Fe deficiency reduced serum FT3 and FT4 concentrations and TPO activity [39, 49].