Glycosylated haemoglobin as an indicator of diabetes control in pregnancy: A 10-year review of the relationship between HbA1c trends and delivery outcome in type I and type II diabetes.

Background: Pregestational diabetes mellitus (PGDM) confers an increased risk of adverse maternal and neonatal outcomes [1,2]. Glycaemic control in the medium and long term is commonly evaluated by examining glycosylated haemoglobin (HbA1c) levels. However, the value of HbA1c in pregnancy may be diminished by increased level of red cell turnover characteristic of pregnancy [3,4]. We sought to examine the impact of HbA1c in the first trimester and pre-delivery, and the within-patient change throughout gestation on mode of delivery and birthweight in pregnancies complicated by a pre-pregnancy diagnosis of type I or type II diabetes.
Methods: A 10-year consecutive cohort of pregnancies complicated by PGDM, from Jan 2010 until Dec 2019, was examined for HbA1c data in the first trimester and within 6 weeks of delivery. Perinatal outcome data, including gestational age at delivery, mode of delivery and birthweight centile, were obtained from hospital records. The Spearman Rank correlation was used to correlate HcA1c levels in the first trimester with birthweight centiles. Non-parametric summaries and rank-based tests, Signed-rank test and Kruskal-Wallis test, were used to compare Hba1c levels.
Results: During the 10-year study period, a consecutive cohort of 396 pregnancies that attained a viable gestational age (>24 weeks' gestation) and complicated by pregestational diabetes was identified; representing 81 % of the population of pregestational diabetic pregnancies managed by this service during the study period. The median [IQR] HbA1c levels (mmol/mol) in the first trimester, pre-delivery and the differential across gestation were 51 [19] mmol/mol, 43 [11] mmol/mol and -8 [13] mmol/mol, respectively. A statistically significant reduction in HbA1c levels throughout gestation was observed (p < 0.001). The median [IQR] birthweight centile was 69 [50 - 96]. The distributions in HbA1c levels and birthweight centiles were heavily skewed. No correlation was identified between HbA1c levels and mode of delivery.
Conclusion: Neither baseline HbA1c levels, pre-delivery values, nor trends across gestation appear to impact birthweight centile or mode of delivery in PGDM. While optimising glycaemic control can affect the long term health of the mother, these indices cannot be relied upon to reflect the impact of glycaemic control on fetal growth aberrations that influence mode of delivery.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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