Desmopressin normalizes severe polyuria in pregnant woman with rare AVP deficiency

Establishing a differential diagnosis for polyuria and polydipsia during pregnancy is challenging, as conditions like gestational diabetes must be carefully excluded. The antidiuretic hormone arginine vasopressin (AVP), also known as ADH, plays a crucial role in water balance. Pregnancy can rarely lead to AVP deficiency due to elevated placental vasopressinase activity, an enzyme that degrades AVP. This condition, known as gestational diabetes insipidus, presents a diagnostic dilemma, especially when standard diagnostic tests like water deprivation are contraindicated in pregnancy, necessitating alternative diagnostic approaches and effective, safe treatments.

A pregnant woman presented with severe polyuria (urine output 9L/24h) and polydipsia without pre-existing symptoms. Gestational diabetes and electrolyte disturbances were excluded, with HbA1c and daily glucose profiles being normal. Due to pregnancy, standard diagnostic tests like water deprivation or arginine stimulation were not performed. Copeptin, a stable surrogate marker for AVP/ADH secretion, was measured. Given disabling symptoms, a trial of oral desmopressin was initiated during admission. Weight, diuresis, plasma/urine sodium, and osmolality were closely monitored throughout treatment. Post-delivery, desmopressin was discontinued, and the patient was monitored for symptom resolution and copeptin levels.

The patient's copeptin level, a surrogate marker for AVP/ADH, was found to be <2 pmol/L (reference range: 0-9 pmol/L), effectively ruling out AVP resistance. This low copeptin level strongly indicated an AVP deficiency. A trial of oral desmopressin during admission led to a complete normalization of diuresis and resolution of thirst, confirming the diagnosis and efficacy of treatment. Close monitoring showed stable weight, plasma/urine sodium, and osmolality. > After delivery of a healthy son, desmopressin was discontinued, and the patient's symptoms resolved spontaneously, with copeptin levels remaining normal, which definitively ruled out primary polydipsia. This clinical course confirmed a diagnosis of pregnancy-induced AVP deficiency due to elevated placental vasopressinase activity, a rare condition affecting 2-4 per 100,000 pregnancies.