Hyponatraemia is defined in pregnancy as a serum sodium below 130mmol/L, and is considered severe below 120mmol/L (reference range 130-140 mmol/L)(1). It can be associated with a high rate of morbidity and mortality, and is therefore important to recognize and correct appropriately to avoid harm(2). Severe hyponatremia is uncommon in pre-eclampsia, but has been reported in the literature arising secondary to hypervolemia or syndrome of inappropriate antidiuretic hormone secretion (SIADH)(3). In this case we report a patient with severe hyponatremia in the context of maternal mirror syndrome, not previously reported. Mirror syndrome is a rare complication of fetal hydrops, characterized by the development of maternal oedema that “mirrors” oedema of the fetus and placenta (4). It is also associated with hypertension and proteinuria, and may be a variant of pre-eclampsia (4). In this case hydrops was secondary to a partial molar pregnancy resulting from fetal diandric triploidy.
The patient was a 35 year old G2P1 who presented at 16 weeks gestation with increasing shortness of breath on exertion, nausea, headaches, weight gain of 10kg over two weeks, and recurrent vaginal bleeding since 12 weeks. She had no significant medical history and her previous pregnancy was uncomplicated.
On presentation, mirror syndrome was diagnosed in the context of significant maternal oedema (bilateral pleural effusions, ascites and pitting oedema), hypertension (150/100 mmHg) and severe hyponatraemia (serum sodium 108mmol/L). Tertiary ultrasound confirmed a single live fetus with hydropic features and a grossly hydropic placenta covering the cervical os. Partial molar pregnancy was suspected.
The issues this case report will address include management of severe hyponatraemia and pre-eclampsia, termination of a non-viable pregnancy in the context of a low lying hydropic placenta, and follow up of a molar pregnancy. In addition, earlier detection of the molar pregnancy may have prevented the acute presentation and associated morbidity. We will also discuss the diagnosis and aetiology of hyponatraemia in pre-eclampsia and mirror syndrome.