Selenium (Serum / Plasma)
Trimester-Specific Reference Ranges
Selenium is an essential micronutrient involved in antioxidant activity, thyroid hormone metabolism, and immune function. Levels tend to fall during pregnancy due to hemodilution and fetal transfer.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| µg/L | 63–160 | 116–146 | 75–145 | 71–133 |
| µmol/L | 0.80–2.03 | 1.47–1.85 | 0.95–1.84 | 0.90–1.69 |
Physiologic changes in pregnancy
- Hemodilution decreases measured serum selenium.
- Placental transport results in maternal → fetal transfer.
- Oxidative stress and increased metabolic demand raise selenium utilization.
- Lower selenium has been linked in some studies to preeclampsia and thyroid dysfunction.
Causes of low selenium
- Poor dietary intake (low-selenium soil regions)
- Malabsorption (celiac disease, Crohn disease)
- Bariatric or gastrointestinal surgery
- Parenteral nutrition without supplementation
- Chronic illness or systemic inflammation
- Nephrotic syndrome (urinary losses)
- Pregnancy-related hemodilution
Causes of high selenium
- Excessive supplementation
- Dietary excess in high-selenium geographic regions
- Environmental/industrial exposure (rare)
- Selenosis (hair/nail changes, metallic taste, neurologic symptoms)
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31. PMID: 19935037
- Rayman MP. Selenium and human health. Lancet. 2012;379:1256–68.
- Williams Obstetrics, 26th ed. Trace minerals in pregnancy.