Introduction:
Mild hyponatremia is common during pregnancy due to physiologic changes
of pregnancy [1]. During pregnancy, physiologic changes occur in
volume- and osmoregulation that effect plasma osmolality and sodium
concentration. In healthy pregnancy, the average plasma-osmolality is
decreased by 5-10 mmol and the sodium concentration is decreased by 5
mmol/l [2]. Typically, this kind of hyponatremia is asymptomatic and
these changes resolve on their own after delivery. The cause of
hyponatremia in pregnancy is mainly due to water retention following
neuro-hormonal changes during pregnancy. It has been stated that high
levels of estrogen and progesterone in pregnancy can exacerbate the
neurological symptoms of hyponatremia as they inhibit the maternal
brain’s sodium pump [3]. These changes result in a decrease in
osmolality, and therefore, the threshold for the hypothalamic secretion
of ADH and the threshold for thirst is reset to a lower plasma
osmolality level, creating a hypo-osmolar state characteristic of
pregnancy.
Symptoms of hyponatremia can vary depending on severity. It can be
asymptomatic or present with headaches, nausea, dizziness, seizures, and
even death. Mild hyponatremia is mostly overlooked as it presents with
nausea and weakness, overlapping with symptoms of pregnancy. As sodium
and water diffuse across the placenta, the fetus is also at risk of
hyponatremia. This can be associated with respiratory distress, feeding
problems, and seizures showing that a hyponatremia baby was delivered
[1].