Homocysteine (Plasma)
Homocysteine is a sulfur-containing amino acid involved in methylation pathways and dependent on folate, vitamin B12, and vitamin B6. During pregnancy, plasma homocysteine levels typically decrease due to hemodilution and increased fetal–maternal vitamin utilization.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| µmol/L | 0 – 12 | 3.34 – 11 | 2 – 26.9 | 3.2 – 21.4 |
Physiology note: Pregnancy-associated reductions in homocysteine are driven by plasma volume expansion and increased utilization of folate and cobalamin for fetal growth.
Causes of low homocysteine in pregnancy
- Physiologic hemodilution of pregnancy
- High folate intake or prenatal vitamin supplementation
- Vitamin B6 supplementation
- Low methionine intake
- Hypothyroidism (mild lowering)
- Rare inborn errors of sulfur amino acid metabolism
Causes of high homocysteine in pregnancy
- Folate deficiency
- Vitamin B12 deficiency
- Vitamin B6 deficiency
- Methylenetetrahydrofolate reductase (MTHFR) polymorphisms
- Chronic kidney disease or renal insufficiency
- Hypothyroidism
- Smoking
- Medications (methotrexate, antiepileptics)
- Malabsorption (celiac disease, gastric bypass)
References
- Kratz A, Ferraro M, Sluss PM, Lewandrowski KB. N Engl J Med. 2004.
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009.
- Murphy MM et al. Clin Chem. 2004.
- Vollset SE, Refsum H et al. Am J Clin Nutr. 2000.