Monoclonal insulin autoimmune syndrome in pregnancy and postpartum

In insulin autoimmune syndrome (IAS), high levels of anti-insulin antibodies cause hypoglycemic episodes. Pregnancy in patients with IAS raises several concerns. The mother may experience glucose imbalances affecting the mother and fetus, transfer of antibodies may induce glucose disturbances in the fetus, and the antibodies may cause IAS in the newborn child. We present the first case of pregnancy and the postpartum period in monoclonal IAS, discuss pathogenetic mechanisms, and recommend how to handle future cases. A patient with monoclonal IAS was treated successfully with daratumumab to decrease anti-insulin antibodies from 1,840 U/mL (<0.4) to 180 U/mL. Treatment was paused to facilitate pregnancy, and after four months she conceived. Her antibody levels remained stable, and she was euglycemic during her pregnancy. The fetus grew at a normal rate. At delivery, the anti-insulin antibody level in the mother was 74 U/mL. The newborn had a level of 38 U/mL, which disappeared within 21 weeks. The child experienced no abnormal glucose fluctuations. The mother's IAS relapsed a few days postpartum, with hypoglycemia and anti-insulin antibody levels rising to 946 U/mL. Treatment with daratumumab was resumed efficaciously. The pregnancy went well for the mother, fetus, and child, probably mainly because of the relatively low levels of anti-insulin antibodies. We discuss possible explanations for the recurrence of IAS in the mother postpartum.