Fulminant type 1 diabetes mellitus in a GDM pregnancy: early recognition is vital for maternal and fetal outcomes

Fulminant type 1 diabetes mellitus (FT1DM) is characterised by extremely rapid destruction of pancreatic beta cells. An association between FT1DM and pregnancy has been reported and can lead to unfavourable pregnancy outcomes without timely treatment. We report a case of FT1DM in a pregnancy with gestational diabetes mellitus (GDM), the first of its kind in the English literature to date. A 27-year-old woman with insulin-requiring GDM presented with rapidly deteriorating glycaemic control in her third trimester of pregnancy despite good concordance to treatment. The investigation identified the hallmarks of FT1DM: hyperglycaemia with acute metabolic decompensation and non-immune-mediated beta-cell failure. She received prompt treatment with intravenous insulin therapy and was transitioned to subcutaneous insulin once biochemical improvement had been achieved, albeit with higher insulin requirements than before. She had a good pregnancy outcome and delivered a healthy male infant 5 weeks later through induction of labour. Due to persistent beta-cell dysfunction, she remained on basal-bolus insulin postpartum. This case highlights the importance of early recognition and treatment of FT1DM in pregnancy to prevent adverse maternal and fetal prognoses. Learning points Fulminant type 1 diabetes mellitus (FT1DM) is a subtype of type 1 diabetes characterised by extremely rapid beta-cell destruction, leading to abrupt-onset hyperglycaemia with ketosis or ketoacidosis. The pathognomonic characteristics of FT1DM include the development of diabetic ketosis or ketoacidosis typically within 7 days after the onset of symptoms of hyperglycaemia, a near-normal level of glycated haemoglobin despite elevated plasma glucose levels and the absence of islet cell autoantibodies. The pathophysiology of FT1DM is unclear but the association with genetic predisposition, viral infection and pregnancy has been reported. Due to its predilection for pregnancy, clinicians should have a high index of suspicion for FT1DM in pregnant women with rapidly progressing hyperglycaemic ketoacidosis. As diabetic ketoacidosis in pregnancy is associated with adverse maternal and fetal outcomes, immediate initiation of treatment in pregnant women with suspected FT1DM is extremely vital to prevent morbidity and mortality, even if investigations are still underway. Patients with FT1DM require lifelong insulin therapy due to the complete loss of beta-cell function.