Hemoglobin (Whole Blood)
Hemoglobin concentration normally decreases during pregnancy due to plasma volume expansion exceeding red cell mass increase (“physiologic dilutional anemia”). Gestational age, iron status, folate/B12 levels, and underlying hematologic disease must be considered.
| Units | Nonpregnant Female | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| g/dL | 12 – 15.8 | 11.6 – 13.9 | 9.7 – 14.8 | 9.5 – 15 |
| g/L | 120 – 158 | 116 – 139 | 97 – 148 | 95 – 150 |
Causes of low hemoglobin in pregnancy
- Iron deficiency anemia (most common)
- Physiologic hemodilution of pregnancy
- Folate or vitamin B12 deficiency
- Chronic blood loss
- Hemoglobinopathies (sickle cell disease, thalassemia)
- Chronic kidney disease (reduced erythropoietin)
- Bone marrow suppression (malignancy, aplastic anemia)
- Hemolysis (HELLP, autoimmune hemolysis, G6PD deficiency)
- Anemia of chronic disease
Causes of high hemoglobin in pregnancy
- Dehydration and hemoconcentration
- Smoking
- High altitude residence
- Chronic hypoxia (cardiac or pulmonary disease)
- Polycythemia vera (rare)
- Use of exogenous erythropoietin
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009.
- ACOG Practice Bulletin No. 233. Anemia in Pregnancy. 2021.
- Milman N. Ann Hematol. 2011.
- Peña-Rosas JP et al. Cochrane Database Syst Rev. 2015.
- WHO. Haemoglobin concentrations for diagnosis of anaemia. 2011.
- Pavord S et al. Br J Haematol. 2020.