Introduction:
Diabetes insipidus during pregnancy is a rare medical problem characterised by polyuria and polydipsia. It is underdiagnosed because increased water intake and polyuria are often considered normal in gestation. Physiologically, there is an increase in vasopressinase produced by the placenta resulting in increased clearance of antidiuretic hormone from 8 weeks to mid-gestation before a peak in the third trimester. The level of vasopressinase declines after birth and symptoms of polydipsia and polyuria usually resolve by 2 month postpartum.
Case Presentation
A 33 year old woman reported increased thirst, polyuria and nocturia in her second pregnancy during her antenatal visit for Gestational diabetes (GDM). She was drinking up to 12 litres of fluids daily. Routine screening test at 27 weeks gestation was diagnostic of GDM. She had maintained good glycaemic control with dietary therapy. In retrospect, she recalled developing polydipsia and polyuria in the latter half of the first pregnancy five years prior. The symptoms had persisted postpartum but were exacerbated during this pregnancy. Her attempts of water restriction led to sensation of dehydration and disorientation and despite fluid restriction, nocturia had persisted. Biochemical test at 33 weeks gestation showed serum osmolality of 297 mOsml/kg (275-295) and urine osmolality of 61 mOsm/kg (50-1500). Repeat measurement ten days later showed serum osmolality of 288 and urine osmolality of 68. She was commenced on Desmopressin Nasal Spray 10ug twice a day at 36 weeks gestation. She had a good response with decrease in polydipsia and polyuria and had a normal vaginal delivery at 40 weeks. The clinical history, biochemistry and immediate response to desmopressin supports the diagnosis of Diabetes Insipidus in gestation.
Conclusion:
This case demonstrates that polydipsia and polyuria in pregnancy should not always be attributed to pregnancy itself and are not features of GDM. We hope to increase awareness in clinicians of this uncommon condition.
Dr Kamala Guttikonda (MBBS FRACP, Endocrinologist, Northern Beaches Hospital, Frenchs Forest, NSW), Dr Xiran He (MBBS BSc, General Medicine and Geriatric Advanced Trainee, North Shore Local Health District NSW Health, NSW)