Discussion:
Maternal hyponatremia is an important yet unrecognized cause of seizure during the peripartum period. As discussed above, specific physiological changes, as well as management practices during the peripartum period can contribute to maternal and neonatal hyponatremia
Hyponatremia is common during pregnancy and but sodium levels as low as 115 mmol/L are extremely rare. A prospective study in 2008 which included 287 women at the time of labor determined that approximately 7% of women had a plasma sodium concentration of 130 mmol/L or lower.[3] The study correlated the hyponatremia to fluid volume administered during labor and not due to oxytocin or epidural analgesia.[3] Similar to our patient, the patients’ with hyponatremia in the study also required device assistance or caesarian section for delivery. However, unlike our patients, none of them experienced a grand mal seizure.
In our search, we have uncovered only six other reported cases of severe hyponatremia in laboring mothers resulting in neurological sequelae[3] [4][5][6][7][8]. The interesting issue in our case is that it is the second reported case where fluid loading contributed to the patient’s hyponatremia was purely via oral free water intake. Furthermore, this case is only case where oral free water intake caused multiple grand-mal seizures during the peripartum period.  In the five other cases, fluid supplementation was with oral intake of water and electrolyte drinks as well as with intravenous fluid and incidental additional fluid via required oxytocin infusion.
Our patient suffered from seizures due to an acute intoxication of water causing acute hyponatremia. The patient was advised by the midwife to increase her water intake as she was getting closer to term “to clean the baby”. Acute hyponatremia can result in neurological symptoms due to the water movement into the brain resulting in cerebral edema which can manifest as seizures, altered mental status, and in severe cases, even coma and death [9]. These changes are typically brought on less than 48 hours. In chronic hyponatremia, neurological changes are very subtle, and patients are typically asymptomatic as the brain adapts to the changes over a longer duration of time (greater than 48 hours) by generating ionogenic osmoles [3]. This mechanism protects the brain by reducing the risk of cerebral edema and therefore, the risk of seizures.
During labor, water intoxication could also occur due to ADH-like-action of oxytocin. Oxytocin and ADH are both released from the posterior pituitary gland are structurally similar which could also result in water retention as it stimulated the ADH receptors of the kidney [3]. Oxytocin is primarily given to help augment labor [10]. There have also been cases reported of water intoxication due to intravenous oxytocin infusion in normal pregnant women that resulted in severe hyponatremia and a grand-mal seizure [11]. Although our patient did not receive intravenous oxytocin, there is a natural release of oxytocin that occurs during delivery which also could have played a role in this acute hyponatremic setting of our patient that further exacerbated the hyponatremia.
Although our patient presented with features mimicking eclampsia during labor, she had no history of pre-eclampsia. Eclampsia is a life-threatening, pregnancy-related multi-organ disorder that manifests as unexplained seizures after 20 weeks of gestation due to abnormal placental development in a patient with a history of pre-eclampsia [12]. Pre-eclampsia is characterized by a prior history of hypertension, proteinuria, thrombocytopenia, and liver dysfunction [12].