Central diabetes insipidus in pregnancy
Jarvis S, Nelson-Piercy C, Dhanjal MK, McCarthy A, Cheng F and Williamson C
Introduction: Diabetes insipidus is rare and affects 1 in 30,000 pregnancies. Although many cases predate the pregnancy, diabetes insipidus can develop de novo. Vasopressin normally acts as a fetal-placental vasoconstrictor and placental vasopressinase degrades and increases its clearance. Increasing vasopressinase activity occurs with advancing gestation and falls by 25% per day postpartum and is undetectable by 2-4 weeks post-delivery. Management of central diabetes insipidus (CDI) and transient diabetes insipidus of pregnancy can be achieved with 1-deamino-8-D-arginine vasopressin (DDAVP), a vasopressin analogue, safe in pregnancy.
Cases: Here, three cases of CDI in pregnancy are presented. All cases predated the pregnancy, two were idiopathic and the other had head trauma-induced CDI and hypopituitarism. One case is currently in the first trimester of pregnancy on treatment but had two successful pregnancies prior to formal diagnosis in which symptoms worsened without DDAVP. In two of the women with CDI, live infants with normal birth-weight were delivered at our unit. Both required induction of labour post-dates (41-42 weeks’ gestation) and augmentation using Syntocinon. During pregnancy, serum sodium levels tended to rise with advancing gestation and DDAVP doses was up titrated. Fetal growth scans demonstrated normal growth velocity and amniotic fluid indices. Maternal blood pressure was stable and none developed pre-eclampsia.
In the postpartum period, DDAVP treatment returned to pre-pregnancy doses with normal sodium levels immediately after delivery. However, by D2-4 postpartum, serum sodium levels <130 mmo/l developed in both cases which subsequently normalised within 2 days in one patient but persisted for 2 weeks in the other. It is noteworthy that both patients breastfed, and lactation may act as a non-osmotic stimulus for vasopressin release through a vasovagal reflex.2
Conclusion: Multidisciplinary working with obstetricians, obstetric physicians and anaesthetists, midwives and consultant endocrinologists is critical to facilitate safe handling of patients with pre-existing CDI in pregnancy. Careful monitoring of the patient's fluid balance, serum sodium and liver enzymes, whilst screening for pre-eclampsia and oligohydramnios are essential. Variable rates of decline in vasopressinase post delivery suggest that it is prudent to check serum sodium more regularly in the first few weeks postpartum until stability is reached.