The Incidence, Characteristics, Management and Outcomes of Peripartum Hyponatraemia in the United Kingdom: A Prospective Study Using the UK Obstetric Surveillance System (UKOSS).

OBJECTIVE

To determine the national incidence, characteristics, management and outcomes of peripartum hyponatraemia.

DESIGN

Prospective, observational study using United Kingdom (UK) Obstetric Surveillance System (UKOSS) methodology.

SETTING

192 of the 194 consultant-led obstetric units in UK National Health Service (NHS) hospitals.

POPULATION: Peripartum UK obstetric admissions.

METHODS

Units submitted cases monthly to UKOSS (April 2019-September 2020). The case definition was symptomatic hyponatraemia (sodium < 125 mmol/L) in labour or ≤ 48 h postpartum, excluding other causes of symptoms. Pre-eclampsia was excluded as a separate aetiology of hyponatraemia and potential cause of symptoms. As symptom documentation varied, characteristics, management and outcomes were compared between cases with and without reported symptoms.

MAIN OUTCOME MEASURES: Demographics, symptoms, labour details, management and outcomes.

RESULTS

Eighty cases were submitted. We excluded 23 cases (10 with sodium ≥ 125 mmol/L and 13 with pre-eclampsia). A further 25 had sodium < 125 mmol/L with no symptoms documented. Thirty-two met the UKOSS definition, resulting in an estimate of 3.0 cases of peripartum hyponatraemia with documented symptoms per 100 000 maternities (95% confidence interval 2.0-4.1), using a national estimate of 1 050 915 maternities across the study period. Characteristics and outcomes of cases with and without documented symptoms had some variation; 53% versus 24% had critical care admissions, 41% versus 40% had neonatal unit admissions, and 38% versus 20% had spontaneous vaginal birth.

CONCLUSIONS

Peripartum hyponatraemia was associated with maternal morbidity. Neonatal morbidity and operative birth were high, even without documented maternal symptoms. Poor recognition and documentation of symptoms have likely underestimated the incidence.