A recent study, reporting hyponatraemia in 9.7% of patients with pre-eclampsia, suggests it occurs more often than the small number of published cases would indicate (1).
Hyponatraemia in pregnancy is defined as a serum sodium of less than or equal to 130 mmol/L (2), and can lead to significant neurological complications (3). Fluid management is identified as an important area of care for women with preeclampsia, but sodium measurement is not considered in the Australasian or UK guidelines (4,5).
We present further evidence that preeclampsia associated hyponatraemia is more common than previously thought.
To investigate the rate and management of antenatal hyponatraemia (Na <130 mmol/L) in women with preeclampsia.
We conducted a retrospective review of cases electronically coded for preeclampsia over a 12 month period and reviewed those with an antenatal sodium recorded at <130 mmol/L.
346 cases of preeclampsia between January 2017 and January 2018 were identified, of which 18 had hyponatraemia recorded before delivery. Patients had a median age of 34 years (range 29-41 years) and were predominately primiparous (84%) with a singleton pregnancy (89%). The lowest serum sodium recorded was 123 mmol/L, but in only three cases were relevant osmolalities investigated after physician review. Management of 47% involved intravenous magnesium and 94% were given antihypertensive medications. 61% required a caesarean section. 20 live infants were born with a median birth weight of 2618g, of which half were admitted to NICU.
The rate of antenatal hyponatraemia in women diagnosed with pre-eclampsia was 5.2%. Although our results from a tertiary referral centre are not representative of the general antenatal population, they strengthen the association between hyponatraemia and preeclampsia.
Hyponatraemia associated with preeclampsia is more common than thought, and further research is required to inform guidelines on appropriate monitoring.