[Pregnancy and thirst, a remarkable duo]

Establishing a differential diagnosis for polyuria and polydipsia during pregnancy can be challenging. We describe a pregnant woman with severe polyuria (urine output 9L/24h) and polydipsia without pre-existing symptoms. Gestational diabetes and electrolyte disturbances were excluded; HbA1c and daily glucose profiles were normal. Due to pregnancy, no water deprivation or arginine stimulation test was performed. Copeptin, a surrogate marker for AVP/ADH, was <2 pmol/L (reference: 0-9 pmol/L), ruling out AVP resistance. Because of disabling symptoms, a trial of oral desmopressin was initiated during admission, leading to complete normalization of diuresis without thirst. Weight, diuresis, plasma/urine sodium, and osmolality were closely monitored. After delivery of a healthy son, desmopressin was discontinued and symptoms resolved spontaneously, with copeptin remaining normal. These findings ruled out primary polydipsia. Conclusion: this was a case of pregnancy-induced AVP deficiency due to elevated placental vasopressinase activity, a rare condition (2-4 per 100,000 pregnancies).