What is the management approach for anemia in a pregnant woman?

Management of Anemia in Pregnancy

Screen all pregnant women with hemoglobin and hematocrit at the first prenatal visit, and start low-dose oral iron supplementation (30 mg/day elemental iron) immediately for primary prevention, regardless of anemia status. 1

Understanding Anemia Throughout Pregnancy

Physiologic Changes and Diagnostic Thresholds

Pregnancy causes physiologic hemodilution that progressively lowers hemoglobin concentration, making diagnosis challenging. 2 The diagnostic thresholds for anemia vary by trimester:

• First trimester: Hemoglobin <11.0 g/dL 1, 3
• Second trimester: Hemoglobin <10.5 g/dL 1
• Third trimester: Hemoglobin <11.0 g/dL 1, 3

Critical pitfall: Hemoglobin or hematocrit alone cannot accurately diagnose iron deficiency in pregnancy due to physiologic hemodilution, and sensitivity/specificity for detecting iron deficiency anemia are unknown. 2

Prevalence and Risk Factors

Iron deficiency affects 18.6% of pregnant women overall, increasing from 6.9% in the first trimester to 29.5% in the third trimester. 2, 3 Importantly, only 16.2% of iron-deficient pregnant women meet criteria for anemia, meaning standard hemoglobin screening misses the majority of cases. 3

Risk factors include:

• Non-Hispanic Black and Mexican American ethnicity 2
• Vegetarian diet lacking adequate iron sources 2
• Gastrointestinal disease or medications reducing iron absorption (e.g., antacids) 2
• Short interpregnancy interval 2
• Parity ≥2 2

Diagnostic Approach

Initial Screening

Measure hemoglobin/hematocrit at the first prenatal visit for all pregnant women. 3 However, recognize that normal hemoglobin does not exclude iron deficiency, as symptoms occur before anemia develops. 3

Confirming Iron Deficiency

When hemoglobin is low or symptoms suggest iron deficiency despite normal hemoglobin, check serum ferritin to confirm iron deficiency (ferritin <30 μg/L). 1, 3

Important caveat: Serum ferritin is an acute phase reactant that increases during inflammation, potentially masking true iron deficiency. 2, 1 Its concentration may also decrease in late pregnancy despite adequate bone marrow iron stores. 2

Treatment Algorithm

First-Line: Oral Iron Supplementation

For confirmed iron deficiency anemia (Hb <11 g/dL): Prescribe 60-120 mg elemental iron daily, taken between meals. 4, 3

For iron deficiency without anemia: Start 30 mg elemental iron daily. 3

For primary prevention in all pregnant women: Begin 30 mg elemental iron daily at the first prenatal visit. 4, 1

Reassess hemoglobin after 4 weeks of treatment, expecting an increase of ≥1 g/dL or hematocrit increase of ≥3%. 4, 3

When Oral Iron Fails

Consider intravenous iron in the second or third trimester only when: 4

• Oral iron fails after 4 weeks despite confirmed compliance and absence of acute illness
• Gastrointestinal side effects prevent oral iron tolerance
• Hemoglobin <10 g/dL after 13 weeks gestation 4

Absolute contraindication: Avoid IV iron in the first trimester due to insufficient safety data. 4, 1 Oral iron is the only recommended treatment during this period. 4

IV Iron Administration Guidelines

After 13 weeks gestation, IV iron may be administered with the following precautions: 4

• Have resuscitation facilities available due to potential hypersensitivity reactions and fetal bradycardia 4
• Fetal monitoring during or after IV iron administration is not required or recommended 4
• Avoid ferric carboxymaltose in patients requiring repeat infusions due to treatment-emergent hypophosphatemia 4
• Monitor phosphate levels post-infusion if ferric carboxymaltose is used 4
• Do not check iron parameters within 4 weeks of IV iron administration, as circulating iron interferes with assays 4

Severe Anemia Requiring Referral

Refer to a physician familiar with anemia in pregnancy when hemoglobin is <9.0 g/dL or hematocrit is <27.0%. 4, 3 Severe anemia carries significant risks including intrauterine growth restriction, prematurity, and increased peripartum blood loss. 3

Maternal and Fetal Consequences of Untreated Anemia

Maternal Complications

• Increased mortality risk 5
• Susceptibility to infections 5
• Preterm labor 5
• Postpartum hemorrhage 5, 6
• Cardiac complications 5
• Impaired neurocognitive function and mood disturbances even before anemia develops 3

Fetal Complications

• Intrauterine growth restriction 3, 5
• Low birth weight 3, 5
• Small-for-gestational-age 3
• Preterm delivery 3, 5
• Stillbirth 3
• Early neonatal death 3
• Impaired fetal brain development 3
• Long-term neurodevelopmental impairments 5

Common Pitfalls to Avoid

Do not dismiss symptoms when hemoglobin is "normal." Iron deficiency causes impaired neurocognitive function, mood disturbances, and dizziness before anemia develops, and standard screening misses iron deficiency without anemia. 3

Verify patient compliance with oral iron. Gastrointestinal side effects frequently lead to discontinuation. 4 If compliance is confirmed but treatment fails after 4 weeks, consider IV iron (after first trimester). 4

Do not rely solely on hemoglobin/hematocrit for diagnosis. Physiologic hemodilution makes these measurements imprecise for detecting iron deficiency. 2, 4