Endocrine Abstracts

A 33-year-old woman (G2P1) was referred to our combined obstetric–endocrine clinic at 23 weeks’ gestation with a 12-week history of excessive thirst, polyuria, and nocturia. She had a history of pituitary adenoma resection in 2008, complicated by transient central diabetes insipidus (DI) requiring desmopressin therapy for one year. Current treatment included levothyroxine 75 mg daily, and she used stress-dose hydrocortisone during intercurrent illness. The pregnancy was conceived via ovulation induction. She reported drinking up to 5 litres of water daily and waking to void seven times nightly. Similar symptoms occurred in a prior pregnancy but were not investigated. Investigations revealed a serum osmolality of 288 mOsm/kg, urine osmolality 326 mOsm/kg, sodium 139 mmol/l, and normal glucose tolerance testing. In the context of her pituitary history and clinical presentation, relapsed partial central DI was diagnosed. Oral desmopressin 0.2 mg BD was initiated and increased to TDS with resolution of symptoms. Pregnancy progressed uneventfully under multidisciplinary care. She delivered a healthy male infant by caesarean section at 38+2 weeks’ gestation (3920g). Desmopressin was discontinued immediately postpartum without symptom recurrence; sodium on day 1 postpartum was 139 mmol/l. Pregnancy is associated with increased degradation of arginine vasopressin (AVP) due to placental production of vasopressinase, a cystine aminopeptidase that inactivates AVP. In individuals with underlying hypothalamic–pituitary dysfunction, this increased enzymatic activity may unmask previously compensated central DI. This case highlights the importance of considering relapsed DI in pregnant women with relevant pituitary history to enable timely diagnosis and management.