Are serial ferritin (iron storage protein) measurements useful in pregnancy?

Serial Ferritin Testing in Pregnancy

Serial ferritin measurements are useful in pregnancy for monitoring iron status, as ferritin is the most specific indicator available for detecting depleted iron stores, though interpretation requires caution due to physiological changes during pregnancy. 1

Value of Ferritin Testing in Pregnancy

• Serum ferritin concentration is an early indicator of iron stores status and the most specific indicator available for depleted iron stores, especially when used with other tests to assess iron status 2
• The prevalence of iron deficiency anemia increases significantly throughout pregnancy, ranging from 1.8% in the first trimester to as high as 27.4% in the third trimester, making monitoring essential 1
• Recent research shows iron deficiency (ferritin <15 μg/L) increases dramatically during pregnancy, from 4.5% at 15 weeks to 51.2% at 33 weeks gestation, highlighting the need for monitoring 3

Recommended Testing Approach

• Screening for iron-deficiency anemia is recommended for all pregnant women, ideally with serum ferritin-level screening in the first trimester followed by regular hemoglobin checks at least once per trimester 4
• When hemoglobin screening reveals anemia, ferritin testing should be performed to confirm iron deficiency as the cause 1
• Among women who test positive for anemia based on hemoglobin concentration, a serum ferritin concentration ≤15 μg/L confirms iron deficiency, while >15 μg/L suggests iron deficiency is not the cause 2

Interpretation Challenges and Limitations

• Ferritin concentration often decreases in late pregnancy despite adequate iron stores in bone marrow, making interpretation more challenging 2, 1
• Serum ferritin is an acute-phase reactant; inflammation, infection, or tissue damage can raise its concentration independent of iron status, potentially masking depleted iron stores 2, 1
• Using hemoglobin or hematocrit measurement alone to determine iron deficiency status during pregnancy can be imprecise due to normal hemodilution 2, 1
• The cost of assessing serum ferritin concentration and unavailability of clinic-based measurement methods can hamper widespread use in screening 2, 1

Optimal Ferritin Thresholds

• Traditional ferritin thresholds for iron deficiency (<12 and <15 μg/L) are the most commonly used (68% of studies) but may be insufficient for pregnancy 5
• Recent research suggests higher trimester-specific thresholds: ~25 μg/L during the first trimester and ~20 μg/L during the second and third trimesters 6
• One study found that ferritin <60 μg/L at 15 weeks gestation predicted iron deficiency (ferritin <15 μg/L) at 33 weeks, suggesting early pregnancy testing with higher thresholds may be valuable 3
• Using traditional thresholds (<15 μg/L) may underestimate the true prevalence of iron deficiency throughout pregnancy by approximately 10% 6

Clinical Implications

• Early detection of iron deficiency through serial monitoring allows for timely intervention with iron supplementation 4
• Iron-containing supplements taken pre-pregnancy/early pregnancy are associated with reduced risk of deficiency throughout pregnancy, including the third trimester 3
• For women with confirmed iron deficiency anemia, oral iron therapy should be given as first-line treatment; intravenous iron therapy should be considered for severe anemia, intolerance to oral iron, or when rapid correction is needed 4
• Regular monitoring with serial ferritin measurements helps guide appropriate supplementation and avoid both under-treatment and over-treatment with iron 7