First trimester fasting glucose and glycated haemoglobin cut-offs associated with abnormal glucose homeostasis in the post-partum reclassification in women with hyperglycaemia in pregnancy

Hyperglycaemia first detected during pregnancy is either gestational diabetes mellitus (GDM) or previous undiagnosed diabetes. We aimed to study if there were a first trimester fasting glycaemia (FTG) and a glycated haemoglobin (HbA1c) cut-off values associated with type 2 diabetes mellitus (T2DM) or abnormal glucose homeostasis (AGH) at the post-partum oral glucose tolerance test (OGTT) reclassification. We retrospectively studied a group of pregnant women from the Portuguese National Registry of GDM. Receiver-operating characteristic (ROC) curves were used to determine the best FTG and HbA1c cut-offs to predict T2DM and AGH. We studied 4068 women. The area under the ROC curves (AUC) for the association with T2DM was 0.85 (0.80-0.90) for FTG and 0.85 (0.80-0.91) for HbA1c. The best FTG cut-off for association with T2DM was 99 mg/dL: sensitivity 77.4%, specificity 74.3%, positive predictive value (PPV) 4.8%, and negative predictive value (NPV) 99.5%. The best HbA1c cut-off for association with T2DM was 5.4%: sensitivity 79.0%, specificity 80.1%, PPV 5.7%, and NPV 99.6%. The AUC for the association of FTG and HbA1c with AGH were 0.73 (0.70-0.76) and 0.71 (0.67-0.74), respectively. The best FTG cut-off for predicting AGH was 99 mg/dL: sensitivity 59.4%, specificity 76.2%, PPV 17.0%, and NPV 95.8%. The best HbA1c cut-off was 5.4%: sensitivity 48.7%, specificity 81.5%, PPV 17.8%, and NPV 95.1%. We suggest an FTG of 99 mg/dL and an HbA1c of 5.4% as the best cut-offs below which T2DM is unlikely to be present. Almost all patients with FTG < 99 mg/dL and HbA1c < 5.4% did not reclassify as T2DM. These early pregnancy cut-offs might alert the physician for the possibility of a previous undiagnosed diabetes and alert them to the importance of testing for it after delivery.