Approach to the diagnosis and treatment of hyponatremia in pregnancy.

Hyponatremia is the most commonly encountered electrolyte abnormality. Severe hyponatremia in pregnancy poses diagnostic and therapeutic challenges. Pregnancy involves changes in physiology that affect water and sodium homeostasis. Knowledge of these complex physiologic alterations during pregnancy is critical to managing dysnatremias in pregnancy. This teaching case describes a woman with chronic hyponatremia who presented during pregnancy with worsening hyponatremia. She had an activating vasopressin receptor mutation, which was passed on to her child, and her diagnostic workup is described.