Phosphorus (Inorganic Phosphate), Serum
Maternal phosphate levels change throughout pregnancy due to increased fetal skeletal demand, altered renal handling, and pregnancy-related hormonal changes including PTH, PTHrP, and vitamin D.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 2.5 – 4.3 | 3.1 – 4.6 | 2.5 – 4.6 | 2.8 – 4.6 |
| mmol/L | 0.81 – 1.39 | 1.0 – 1.49 | 0.81 – 1.49 | 0.9 – 1.49 |
Pregnancy physiology
- Phosphate is essential for fetal bone mineralization and growth.
- Maternal renal phosphate excretion increases during pregnancy.
- Levels may rise slightly in early pregnancy due to increased intestinal absorption (vitamin D mediated).
- Mild late-pregnancy reductions can occur from increased fetal utilization.
Reasons for LOW phosphorus
- Poor dietary intake
- Vitamin D deficiency
- Hyperparathyroidism (increased renal phosphate loss)
- Refeeding syndrome
- Diabetic ketoacidosis
- Chronic alcohol use
- Long-term antacid or phosphate-binder use
Reasons for HIGH phosphorus
- Renal insufficiency or acute kidney injury
- Hypoparathyroidism
- High phosphate intake
- Tumor lysis syndrome (rare in pregnancy)
- Hemolysis
- Vitamin D excess
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
- Kovacs CS. Maternal mineral metabolism during pregnancy and lactation. Endocrinol Metab Clin.
- Fusaro M et al. Phosphate metabolism and its clinical relevance. Clin Cases Miner Bone Metab.