Causes of Severe Anemia in Pregnancy
Severe anemia in pregnancy is most commonly caused by iron deficiency, followed by folate deficiency, malaria (in endemic areas), acute blood loss, and less commonly by vitamin B12 deficiency, hemoglobinopathies, and infectious diseases including HIV.
Primary Etiologic Framework
The pathophysiology of severe anemia in pregnancy stems from three fundamental mechanisms that often coexist 1:
- Increased iron demand - pregnancy requires iron for fetal/placental development and maternal erythrocyte mass expansion
- Decreased intake/absorption - inadequate dietary iron, malabsorption from GI disease or medications (antacids)
- Blood loss - hemorrhage during pregnancy or delivery
Most Common Causes by Prevalence
Iron Deficiency (Most Common)
Iron deficiency is the predominant cause, accounting for approximately 92.7% of severe anemia cases in pregnancy 2. The condition develops when body iron stores become so depleted that hemoglobin synthesis is impaired 1. Risk factors include 1:
- Diet lacking iron-rich foods (vegetarian diets with inadequate iron sources)
- Gastrointestinal disease or medications decreasing absorption (antacids)
- Short interpregnancy intervals
- Multiparity (≥2 pregnancies)
- Non-Hispanic Black and Mexican American ethnicity (higher prevalence rates)
Folate Deficiency (Second Most Common)
Folate deficiency affects approximately 62% of severely anemic pregnant women, often secondary to malarial hemolysis in endemic regions 3. This cause is particularly important because it occurs earlier in pregnancy and associates with more severe anemia and low birthweight compared to iron deficiency alone 3.
Malaria (Geographic-Specific)
In endemic areas, Plasmodium falciparum malaria affects 84% of severely anemic pregnant women 3. The anemia results from hemolysis and is typically more severe than iron deficiency anemia, occurring earlier in pregnancy and in younger women 3.
Multiple Pregnancy
Multiple gestation carries an odds ratio of 8.9 (95% CI: 1.1-71.0) for severe anemia due to increased iron demands 4.
Infectious Causes
- Urinary tract infections: OR 6.2 (95% CI: 3.5-11.0) for severe anemia 4
- HIV infection: Associated with severe anemia through multiple mechanisms including malnutrition, opportunistic infections, and direct bone marrow suppression 5. CD4+ count <200/μL carries OR 2.70 for severe anemia 5
- Schistosomiasis: Contributes in endemic regions 4
Nutritional Deficiencies Beyond Iron
- Vitamin B12 deficiency: Uncommon but can cause severe anemia (Hb as low as 3.7 g/dL) 6. Occurs in 10-28% of uncomplicated pregnancies but rarely causes severe anemia
- Low BMI (<20 kg/m²): OR 2.0 (95% CI: 1.2-3.4) for severe anemia 4
- Vitamin A deficiency: Serum retinol <70 μmol/L carries OR 2.45 for severe anemia 5
Hemoglobinopathies
- Sickle cell disease: Must be considered in the differential 3
- Thalassemias: Particularly in at-risk ethnic populations
Hookworm Infection
Contributes to iron deficiency in approximately one-third of patients with nutritional iron deficiency 3.
Critical Clinical Distinctions
Important caveat: The anemia from malaria and folate deficiency is both more common AND more severe than iron deficiency anemia alone, occurs in younger women (though not necessarily primigravidae), presents earlier in pregnancy, and associates with low birthweight 3. This contrasts with the typical teaching that focuses primarily on iron deficiency.
Geographic and Socioeconomic Considerations
The relative importance of causes varies dramatically by setting:
- High-resource settings (U.S./Europe): Iron deficiency predominates, with prevalence ranging from 2-27% depending on trimester and ethnicity 1
- Low-resource settings: Multiple etiologies coexist - malaria, folate deficiency, iron deficiency, infections, and malnutrition all contribute significantly 3, 4, 5
Inadequate Antenatal Care as Risk Factor
Fewer than 4 antenatal clinic visits carries OR 1.9 (95% CI: 1.2-3.0) for severe anemia 4, likely reflecting delayed detection and treatment of treatable causes.
Unusual Cause: Pica
Eating soil during early pregnancy (geophagia) carries OR 2.47 (95% CI: 1.66-3.69) for severe anemia, likely through interference with iron absorption 5.
Key Pitfall to Avoid
Physiologic hemodilution during pregnancy can make determining true anemia prevalence difficult 1. Hemoglobin/hematocrit alone may be imprecise for determining iron deficiency status during pregnancy 1. Therefore, don't rely solely on hemoglobin cutoffs - investigate underlying causes comprehensively, particularly when anemia is severe (Hb <7-8 g/dL).