Background Insulin requirements in women with pre-gestational diabetes have been demonstrated to follow a pattern of initial insulin sensitivity to a progressive resistance with a nadir from 36 weeks [1, 2]. Rare cases of refractory insulin resistance in T1DM due to subcutaneous insulin resistance  have been described outside of pregnancy. This is a case report of potential pregnancy-mediated subcutaneous insulin resistance, requiring management with intravenous insulin therapy.
Case description A 26-year-old female gravida 3 para 2, managed for T1DM preconception on total daily insulin (TDI) of 50 units/day with HbA1c 6.1%, presented with deteriorating glycaemic control from 28 weeks gestation. Her previous pregnancy, at another facility, was complicated by diabetic ketoacidosis at 36 weeks gestation precipitating emergency delivery.
She was admitted at 31 weeks gestation for glycaemic stabilisation and subcutaneous insulin doses were increased rapidly to a peak TDI 394 units, with no improvement in glycaemia. Intravenous insulin was introduced at 32 weeks gestation, resulting in an improved average BGL from 12.1mmol/L to 9.1mmol/L. A re-trial of subcutaneous insulin therapy alone rapidly resulted in hyperglycaemia. Intravenous insulin continued at TDI 170 units, with stable, controlled glycaemia. Before a trial of complete cessation of subcutaneous insulin, the patient prematurely delivered at 34 weeks gestation. Post-partum, normoglycemia was achieved with subcutaneous insulin at TDI 12 units.
Discussion This case presents an unusual phenomenon of refractory hyperglycaemia from 28 weeks gestation, without meaningful improvement from an 8-fold increase in subcutaneous therapy but a clear response to intravenous insulin. The disparity between improvement from intravenous versus subcutaneous insulin therapy may suggest a pregnancy-mediated subcutaneous insulin resistance not previously described in the literature.