Background: Gestational diabetes mellitus (GDM) is a well-known risk
factor for pregnancy complications. While hemoglobin A1c (HbA1c) is widely used
as a glycemic control indicator, it is known to exhibit falsely low or high
levels during gestation. The purpose of the present study is to analyze the
fluctuations in HbA1c levels throughout pregnancy in diabetic (DM) and non-DM
women with or without iron deficiency anemia (A). Methods: Medical
records of pregnant women who were followed up in our obstetrics clinic between
2018 and 2022 were reviewed. Demographics, gestational history, and biochemistry
values including fasting glucose, HbA1c, erythrocyte and iron metabolism indexes
were recorded. Statistical analysis was carried out by Mann-Whitney U and
Bonferroni corrected one-way analysis of variance (ANOVA) tests.
Results: 670 pregnant women (32 14.2 years) were included with
matched subgroups. In the non-DM and non-A group, HbA1c exhibited a significant
decrease towards mid-pregnancy (5.29
vs. 5.08%, p 0.01),
followed by a steep increase towards the second half of pregnancy, reaching its
initial value (5.08 vs. 5.27%, p 0.01). In the non-DM and
A pregnant women, HbA1c decreased from 5.25 to 5.19% (p 0.05) in
first half, followed by a significant increase to 5.37% (p 0.05) in
the second half of pregnancy when serum ferritin values dropped to 5.03 3
µg/mL (p 0.01). As for DM and non-A group, a biphasic
change in HbA1c level was also recorded, however not significant (6.05
vs. 5.81%, p 0.05). However, in the DM and A group, HbA1c
levels were higher (7.09 vs. 6.01%, p 0.01), along with
iron deficiency indicated by ferritin levels (4.7 2.2 µg/mL,
p 0.01). Conclusions: HbA1c exhibits biphasic changes
throughout pregnancy, characterized by decreases towards mid-pregnancy and
subsequentincreases in the third trimester. Therefore, questioning HbA1c levels
is warranted, considering the changes in maternal physiology in early gestation
and the increasing need for iron in later period. Furthermore, iron deficiency
anaemia seems to have significant impact on the reliability of HbA1c in both the
non-DM and DM pregnant women.