Iron (Serum)
Serum iron reflects circulating iron bound primarily to transferrin. Values fluctuate with diurnal variation, recent dietary intake, inflammation, and in pregnancy, with plasma volume expansion and increased fetal iron demand.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| µg/dL | 41 – 141 | 72 – 143 | 44 – 178 | 30 – 193 |
| µmol/L | 7 – 25 | 13 – 26 | 8 – 32 | 5 – 35 |
Clinical note: Serum iron alone is not sufficient to diagnose iron deficiency. Interpret alongside ferritin, transferrin saturation, and hemoglobin.
Causes of low serum iron in pregnancy
- Iron deficiency — most common cause
- Poor dietary intake or malabsorption (celiac disease, IBD)
- Chronic blood loss (pre-pregnancy menorrhagia, GI bleeding)
- Increased iron demand of pregnancy and fetal erythropoiesis
- Anemia of chronic inflammation (hepcidin-mediated iron sequestration)
- Chronic infection or systemic inflammatory disease
Causes of high serum iron in pregnancy
- Hereditary hemochromatosis (rare in pregnancy)
- Iron overload from supplementation or transfusion
- Acute hepatitis or liver injury
- Hemolytic anemia
- Sideroblastic anemia
- Recent large oral or parenteral iron dose (transient elevation)
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009.
- ACOG Practice Bulletin No. 233. Anemia in Pregnancy. 2021.
- Milman N. Iron requirements in pregnancy. J Pregnancy. 2012.
- Weiss G, Goodnough LT. Anemia of inflammation. N Engl J Med. 2005.
- Pavord S et al. UK Guidelines on Iron Deficiency in Pregnancy. Br J Haematol. 2020.