Antepartum A1C, maternal diabetes outcomes, and selected offspring outcomes: an epidemiological review

Abstract

Between 1989 and 2004, the prevalence of gestational diabetes mellitus (GDM) in the United States increased by 122%. Glycated haemoglobin, as measured by haemoglobin A1C (A1C), can potentially identify pregnant women at high risk for adverse outcomes associated with GDM including macrosomia and post-partum glucose intolerance. Our objective was to systematically review the literature with respect to A1C levels during pregnancy and associated maternal and offspring outcomes. We used MEDLINE to identify relevant publications from 1975 to 2009. We included articles if they met the following criteria: original full text articles in English; primary exposure of antepartum A1C; women with GDM at baseline or who developed GDM during the study; primary outcome of GDM, insulin use, post-partum abnormal glucose or type 2 diabetes (T2DM), birthweight, macrosomia or large for gestational age. Case series and case reports were excluded. Twenty studies met our criteria. A1C at GDM diagnosis was positively associated with post-partum abnormal glucose. Women with post-partum T2DM or impaired glucose tolerance had mean A1C at GDM diagnosis higher than those with normal post-partum glucose (P ≤ 0.002) and a 1% increase in A1C at GDM diagnosis was associated with 2.36 times higher odds of post-partum abnormal glucose 6 weeks after delivery [95% confidence interval 1.19, 4.68]. The association of A1C and birthweight varied substantially between studies, with correlation coefficients ranging from 0.11 to 0.51. A1C, a less burdensome and costly measure than an oral glucose tolerance test, appears to be an attractive measure for identifying women at high risk of adverse outcomes associated with GDM.

Figure 1.

Glucose thresholds and equivalent A1C values^a for diagnosis of gestational diabetes (GDM) by the National Diabetes Data Group (NDDG),^b American Diabetes Association (ADA)^b and the World Health Organization (WHO).^{c a} Conversion formula from Nathan et al. glucose (mg/dL) = 1.59*(A1C) −2.59. ^b NDDG and ADA use a 3 h 100 g oral glucose tolerance test, and require two out of four values to exceed the thresholds to diagnose GDM. ^c WHO uses a 2 h 75 g oral glucose tolerance test, and requires one out of the two values to exceed the thresholds to diagnose GDM.