When is repeat ferritin testing indicated in pregnancy?

Repeat Ferritin Testing During Pregnancy

Repeat ferritin testing is indicated in pregnancy when initial values are low (<30 μg/L), when anemia is detected on hemoglobin screening, or in the third trimester for women with initially normal but borderline ferritin levels (<60 μg/L) in early pregnancy. 1, 2

Rationale for Ferritin Testing in Pregnancy

Iron deficiency is a common condition during pregnancy, with prevalence increasing significantly as pregnancy progresses:

• Iron deficiency prevalence increases from 4.5% at 15 weeks to 51.2% at 33 weeks when using the ferritin threshold of <15 μg/L 2
• Using a higher threshold of <30 μg/L, iron deficiency rates increase from 20.7% in the first trimester to 83.8% in the third trimester 2
• The prevalence of iron deficiency anemia ranges from 1.8% in the first trimester to as high as 27.4% in the third trimester 3

Initial Screening Recommendations

• Serum ferritin screening is recommended in the first trimester for all pregnant women 1
• Regular hemoglobin checks should be performed at least once per trimester 1
• Serum ferritin is the most specific indicator available for detecting depleted iron stores 3

When to Repeat Ferritin Testing

1. Low Initial Ferritin Values

• When initial ferritin levels are <30 μg/L, indicating iron deficiency 1
• Follow-up testing is needed to monitor response to iron supplementation 1

2. When Anemia is Detected

• If hemoglobin screening reveals anemia, ferritin testing should be performed to confirm iron deficiency as the cause 3
• A serum ferritin concentration of ≤15 μg/L in an anemic pregnant woman confirms iron deficiency 3

3. Third Trimester Testing

• Even with initially normal values, repeat testing in the third trimester is valuable as iron stores significantly decrease throughout pregnancy 2
• Research shows that ferritin <60 μg/L in early pregnancy predicts iron deficiency (ferritin <15 μg/L) by the third trimester 2

4. After Starting Iron Therapy

• To assess the effectiveness of iron supplementation in restoring iron stores 4
• Women receiving iron supplementation can maintain their iron stores throughout pregnancy, while those without supplementation typically show depleted stores by the third trimester 4

Clinical Significance of Monitoring Iron Status

• Iron deficiency during pregnancy is associated with increased risk of premature labor contractions 5
• Women with serum ferritin values below 10 μg/L had a 48% incidence of premature labor contractions, compared to only 11% in women with values exceeding 20 μg/L 5
• Low iron stores occur with increasing frequency as gestation advances 6

Interpretation of Ferritin Results

• Serum ferritin is an acute phase reactant; levels may increase during inflammation or infection, potentially masking iron deficiency 3
• Ferritin concentration often decreases in late pregnancy despite adequate iron stores in bone marrow, making interpretation more challenging 3
• For women who test positive for anemia based on hemoglobin concentration, a serum ferritin ≤15 μg/L confirms iron deficiency 3

Limitations of Testing

• The cost of assessing serum ferritin and unavailability of clinic-based measurement methods can hamper widespread use 3
• Using hemoglobin or hematocrit measurement alone to determine iron deficiency status during pregnancy can be imprecise due to normal hemodilution 3
• Sensitivity and specificity of hemoglobin/hematocrit for detecting iron deficiency anemia in pregnant women are unknown 3