Effect of iron supplementation on HbA1c levels in pregnant women with and without anaemia

Background: Iron deficiency anaemia has been associated with higher HbA1c levels. However, during and after iron supplementation there is a decrease in HbA1c results, causing a misinterpretation. Our aim was to analyse the effect of iron supplementation on HbA1c levels in nondiabetic pregnant women with and without anaemia. Methods: Pregnant women in prenatal care, without gestational diabetes (GDM) or previous diabetes mellitus (DM) that performed an oral glucose tolerance test (OGTT) in the third trimester of pregnancy were invited to participate. Clinical and laboratorial analyses were performed, including standardized questionnaire, OGTT, full blood count and HbA1c. Results: A total of 231 pregnant women without DM or GDM were included in the study. According to anaemia and/or iron supplementation, we divided women in: no iron and no anaemia - Group 1 (N = 86); no iron and with anaemia - Group 2 (N = 29); iron and no anaemia - Group 3 (N = 87); iron and anaemia - Group 4 (N = 29). There was statistically a significant, although no clinically relevant, difference between HbA1c values in pregnant women in Groups 1 and 4 [5.1 +/- 0.4% (32 +/- 4.4 mmol/mol) and 4.8 +/- 0.3% (29 +/- 3.3 mmol/mol), P < 0.01; respectively]. HbA1c values in pregnant women in Groups 1, 2 and 3 were similar, independently of anaemia [5.1 +/- 0.4% (32 +/- 4.4 mmol/mol); 5.0 +/- 0.4% (31 +/- 4.4 mmol/mol) and 5.0 +/- 0.4% (31 +/- 4.4 mmol/mol); p > 0.05; respectively]. Conclusions: Iron supplementation during pregnancy does not affect HbA1c levels and has no clinical impact in the final interpretation of results in the absence of anaemia or presence of mild anaemia. Interpreting HbA1c results in pregnant women during iron therapy and with moderate or severe anaemia still requires caution.