Potassium (Serum)
Slight decreases are common in pregnancy due to hemodilution, increased glomerular filtration rate, and respiratory alkalosis–driven transcellular potassium shifts.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mEq/L (mmol/L) | 3.5 – 5.0 | 3.6 – 5.0 | 3.3 – 5.0 | 3.3 – 5.1 |
Pregnancy Physiology
- Plasma volume expansion slightly lowers serum potassium concentration.
- Progesterone increases renal blood flow and GFR → increased urinary potassium loss.
- Mild respiratory alkalosis shifts potassium into cells.
- Potassium usually remains in the low-normal range during pregnancy.
- Potassium < 3.0 mEq/L is not physiologic and requires evaluation.
Causes of LOW Potassium (Hypokalemia)
- Hyperemesis gravidarum
- Diarrhea, gastrointestinal potassium losses
- Diuretic therapy
- Renal tubular acidosis
- Primary hyperaldosteronism
- Hypomagnesemia
- Beta-agonists (e.g., terbutaline), insulin therapy
- Corticosteroid therapy
- Excessive intravenous fluid administration (dilutional)
Causes of HIGH Potassium (Hyperkalemia)
- Preeclampsia with renal impairment
- Acute kidney injury
- ACE inhibitors, ARBs, spironolactone
- Hemolysis (pseudo-hyperkalemia)
- Metabolic acidosis
- Adrenal insufficiency
- Massive blood transfusion
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009;114:1326–31.