Although HbA1c is widely used as a glycemic control indicator, HbA1c is known to show falsely high levels in patients in an iron deficient state (IDS). We compared the influence of IDS on HbA1c levels between pregnant women, due to mainly an increase in demand for iron without bleeding, and non-pregnant women, due to mainly bleeding (menstruation). We studied 42 non-diabetic pregnant women (pregnant group) and 42 age-matched non-pregnant women with normal glucose tolerance (non-pregnant group). We compared HbA1c and glycated albumin (GA) levels between IDS and normal iron state (NIS) in both groups. Furthermore, we analyzed the correlation between indicators of glycemic control and iron-related parameters [mean corpuscular hemoglobin, serum transferrin saturation (%Tf), and serum ferritin] in both groups. Compared with non-pregnant women, pregnant women had significantly lower %Tf and serum ferritin levels and significantly higher morbidity of IDS. HbA1c, but not GA, had significantly higher levels in pregnant women with IDS compared with NIS; however, HbA1c in non-pregnant women showed no significant difference for both IDS and NIS. In pregnant women, significant negative correlations were observed between HbA1c and iron-related parameters. In non-pregnant women, negative correlations were observed between HbA1c and these parameters, but they were not significant. No significant correlations were observed between GA and iron-related parameters in both groups. HbA1c levels in pregnant women were found to be largely affected by iron deficiency compared with non-pregnant women. For this reason, GA, which is not affected by iron deficiency, is desirable for use in the assessment of glycemic control during pregnancy.
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