Adverse pregnancy outcomes are more common in women with hyperglycaemia. Many women have suboptimal uptake of HbA1c testing postdelivery. To compare pregnancy outcomes among multi-ethnic women with different degrees of hyperglycaemia during pregnancy, and their association with postnatal HbA1c uptake after the introduction of email reminders. A retrospective and prospective single-centre study was conducted in South Auckland in 2639 women with early gestational diabetes mellitus (GDM) (diagnosed<20weeks), late GDM (diagnosed≥20weeks), overt diabetes in pregnancy, or known type 2 diabetes (T2DM) during pregnancy. Automated email reminders were sent to general practitioners to increase postnatal HbA1c screening. HbA1c during pregnancy increased across the late GDM (n=1425), early GDM (n=148), overt diabetes (n=573) and T2DM (n=493) groups (P<0.001). Stillbirth was least common in the late GDM group (0, 0.7, 0.5, and 1.9%, respectively, P<0.001), as were caesarean delivery (32.7, 45.1, 39.4, and 53.5%, respectively, P<0.001), large for gestational age (LGA) (14.7, 18.2, 22.3, and 30.5%, respectively, P<0.001), small for gestational age (8.8, 16.7, 11.0, and 11.1%, respectively, P=0.02), and preeclampsia/eclampsia (7.7, 9.2, 13.0, and 14.8%, respectively, P<0.001). LGA and preeclampsia/eclampsia were more common among Pacific and Māori women than European women (LGA, 30.1, 22.7, 10.3%, respectively, P<0.001; preeclampsia/eclampsia, 13.5, 14.0, and 8.1%, respectively, P<0.001). Postpartum HbA1c screening increased among women with GDM/overt diabetes after the introduction of the reminder emails (39.6% vs 34.0%, P=0.03). Women with late GDM are least likely to experience adverse outcomes. Email reminders to improve postpartum HbA1c screening warrant further investigation.