Hemoglobin A _1c and postpartum abnormal glucose tolerance among women with gestational diabetes mellitus

OBJECTIVE: To analyze the association of hemoglobin A _1c (HbA _1c) at gestational diabetes mellitus (GDM) diagnosis with postpartum abnormal glucose in a cohort of women with GDM. METHODS: Women with singleton pregnancies treated for GDM at a large diabetes and pregnancy program located in Charlotte, North Carolina, who completed a postpartum 2-hour oral glucose tolerance test were eligible for inclusion in this retrospective cohort study. Clinical information, including maternal HbA _1c at diagnosis, was abstracted from medical records. A parametric survival model was used to assess the association of HbA _1c at GDM diagnosis with postpartum maternal abnormal glucose including impaired fasting glucose, impaired glucose tolerance, and any postpartum abnormal glucose. RESULTS: Of the 277 postpartum women with GDM, 75 (32%) had impaired fasting glucose, 61 (28%) had impaired glucose tolerance, and 15 (9%) were diagnosed with type 2 diabetes mellitus after delivery. After adjustment for clinic, maternal age, parity, prepregnancy body mass index 25 or higher, nonwhite race or ethnicity, and gestational week at first HbA _1c, we detected a trend of increased risk for impaired fasting glucose (P=.01), impaired glucose tolerance (P=.002), and any glucose abnormality (P<.001) associated with increased quartile of HbA1c at GDM diagnosis. CONCLUSION: Hemoglobin A _1c measured at GDM diagnosis may be a useful tool for identifying patients with GDM at highest risk of developing postpartum abnormal glucose. LEVEL OF EVIDENCE: II.