Causes of Hypokalemia in Pregnancy
Hypokalemia in pregnancy results from a combination of physiologic pregnancy-related changes, pathologic gastrointestinal losses (primarily hyperemesis gravidarum), underlying genetic tubular disorders, and medication effects.
Physiologic Causes
- Normal pregnancy induces a natural decrease in serum potassium by 0.2-0.5 mmol/L around midgestation due to hormonal changes and expanded plasma volume 1
- Altered renal tubular function during pregnancy affects electrolyte handling, with increased glomerular filtration and changes in tubular reabsorption 2
- Compensatory renal excretion of bicarbonate occurs in response to pregnancy-induced respiratory alkalosis, which can affect potassium balance 2
Pathologic Gastrointestinal Losses
- Hyperemesis gravidarum is the most common pathologic cause of severe hypokalemia in pregnancy, occurring in approximately 1% of pregnancies and causing fluid volume deficit, metabolic alkalosis, and profound hypokalemia 3, 4
- Severe vomiting leads to direct potassium loss and creates metabolic alkalosis with compensatory renal potassium wasting 5
- Inadequate oral intake due to hyperemesis or poor nutrition compounds the potassium deficit 1
- Hypokalemia from hyperemesis can be severe enough (<2.5 mmol/L) to cause rhabdomyolysis and muscle weakness 3
Genetic Tubular Disorders
- Bartter syndrome causes salt wasting and hypokalemia due to genetic defects in transporters of the thick ascending limb of Henle 1
- Women with Bartter syndrome require increased electrolyte supplementation during pregnancy, with target potassium levels of at least 3.0 mmol/L 1
- Gitelman syndrome similarly causes severe hypokalemia and hypomagnesemia during pregnancy 6
- These genetic disorders are particularly dangerous when combined with hyperemesis gravidarum due to compounded electrolyte disturbances 1
Medication-Related Causes
- Diuretics (particularly potassium-sparing diuretics when discontinued or thiazide/loop diuretics when used) can cause hypokalemia 1
- Medications that exacerbate hypomagnesemia (certain antibiotics, proton pump inhibitors) indirectly worsen hypokalemia since magnesium is required for potassium repletion 1
- Beta-agonists used for tocolysis can shift potassium intracellularly 2
Associated Electrolyte Abnormalities
- Hypomagnesemia frequently coexists with hypokalemia and must be corrected simultaneously, as magnesium deficiency prevents effective potassium repletion 1
- Hypochloremia commonly accompanies hypokalemia in the setting of vomiting-induced metabolic alkalosis 1, 5
- Hyponatremia may occur with severe water ingestion and vomiting 5
Critical Clinical Pitfalls
- Failure to recognize that hypokalemia in pregnancy can be severe enough to cause life-threatening complications including rhabdomyolysis, paralysis, and cardiac arrhythmias 3, 7
- Underestimating the increased potassium demands during pregnancy due to fetal growth 1
- Not screening for underlying genetic tubular disorders in women with recurrent or severe hypokalemia 1, 6
- Treating hypokalemia without simultaneously correcting hypomagnesemia, which renders potassium repletion ineffective 1