Serum Vitamin B12 concentrations typically decrease during pregnancy due to hemodilution, increased fetal utilization, and changes in binding proteins. Reference ranges below reflect trimester-specific values.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| pg/mL | 279-966 | 118-438 | 130-656 | 99-526 |
| pmol/L | 206-713 | 87-323 | 96-484 | 73-388 |
Causes of Low Vitamin B₁₂ in Pregnancy
- Dietary deficiency (vegan/vegetarian diet)
- Pernicious anemia (intrinsic factor deficiency)
- Malabsorption (celiac disease, inflammatory bowel disease)
- Post-gastrectomy or gastric bypass
- Long-term metformin use
- Proton pump inhibitors or H2 blockers (reduced gastric acid)
- Increased fetal and placental utilization
- Dilutional effect from increased plasma volume
Clinical Notes
- Vitamin B₁₂ deficiency in pregnancy can contribute to macrocytic anemia and neurologic symptoms.
- Low B₁₂ may elevate homocysteine and methylmalonic acid.
- Replacement is safe in pregnancy; oral and parenteral regimens are effective depending on etiology.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114(6):1326-1331. PMID: 19935037