How should I evaluate and manage anemia in a pregnant patient?

Evaluation and Management of Anemia in Pregnancy

Screen all pregnant women with a complete blood count (CBC) at the first prenatal visit and again at 24-28 weeks of gestation, using hemoglobin <11 g/dL in the first trimester and <10.5 g/dL in the second/third trimester as diagnostic thresholds for anemia. 1, 2

Initial Screening and Diagnosis

When to Screen

• Obtain CBC at first prenatal visit (first trimester) 1, 2
• Repeat screening at 24-28 weeks of gestation 1, 2
• Screen again at 4-6 weeks postpartum in women at risk for persistent anemia 3, 4

Diagnostic Thresholds

• First trimester: Hemoglobin <11.0 g/dL indicates anemia 2
• Second/third trimester: Hemoglobin <10.5-11.0 g/dL indicates anemia 2
• Note that physiologic hemodilution occurs normally during pregnancy, making hemoglobin/hematocrit alone imprecise for determining iron deficiency status 1

Initial Laboratory Evaluation

The CBC with indices provides critical diagnostic information:

• Mean corpuscular volume (MCV): Low MCV suggests iron deficiency; very low MCV requires further investigation 2, 5
• Red cell distribution width (RDW): Elevated RDW is characteristic of iron deficiency anemia 5
• Hemoglobin concentration: Determines severity and urgency of treatment 2

Classification by Severity and MCV

Mild Anemia (Hemoglobin ≥10.0 g/dL)

With normal or mildly low MCV: Presumptive diagnosis of iron deficiency anemia can be made and oral iron therapy initiated immediately without additional testing 4, 2. A therapeutic trial of oral iron serves as both diagnostic and therapeutic intervention 2.

With very low MCV or macrocytic pattern: Requires further investigation before treatment 2. Consider:

• Serum ferritin (though limited utility in pregnancy as it decreases in late pregnancy despite adequate stores and increases with inflammation) 1
• Hemoglobinopathy screening if not previously done 6
• Vitamin B12 and folate levels if macrocytic 7

Moderate Anemia (Hemoglobin 7.0-9.9 g/dL)

Requires comprehensive evaluation before initiating treatment 2:

• Complete blood count with differential
• MCV and RDW 5
• Serum ferritin concentration 3
• Consider hemoglobinopathy screening 6

Severe Anemia (Hemoglobin <7.0 g/dL or <9.0 g/dL depending on guideline)

Refer immediately to a physician experienced in managing anemia during pregnancy 3, 4. This requires urgent evaluation and may necessitate blood transfusion 6.

Treatment Algorithm

First-Line: Oral Iron Therapy

For established iron deficiency anemia, prescribe 60-120 mg of elemental iron daily 3, 4, 8. Recent evidence supports that intermittent dosing is as effective as daily dosing with fewer gastrointestinal side effects 2.

Treatment protocol:

• Continue oral iron until hemoglobin normalizes for gestational age 3
• Then decrease to 30 mg/day for maintenance 3
• Counsel patients on consuming iron-rich foods and factors that enhance absorption (vitamin C) 3, 4
• Monitor response after 4 weeks: expect hemoglobin increase of 1 g/dL or hematocrit increase of 3% 3, 4

When Oral Iron Fails

If anemia does not respond after 4 weeks despite confirmed compliance, perform additional evaluation 3:

• Verify compliance with oral iron therapy 8
• Measure MCV, RDW, and serum ferritin 3
• Rule out other causes: hemoglobinopathies, vitamin B12/folate deficiency, chronic disease, hemolysis 7, 2
• Assess for gastrointestinal malabsorption 8

Second-Line: Intravenous Iron

Intravenous iron sucrose is indicated when: 8, 9

• Oral iron therapy has failed despite confirmed compliance
• Severe gastrointestinal side effects prevent oral therapy
• Gastrointestinal malabsorption is present
• Gestational age ≥30 weeks with hemoglobin 7-9 g/dL requiring rapid correction
• Hemoglobin <8 g/dL requiring rapid correction

Safety considerations for IV iron: 9

• Published studies after the first trimester show no adverse maternal or fetal outcomes
• Severe hypersensitivity reactions can occur and may cause fetal bradycardia, especially in second/third trimester
• Contemporary formulations have rare allergic reactions 2
• Monitor breastfed infants for gastrointestinal toxicity if used postpartum 9

Special Populations and Considerations

Vegetarian Women

Iron requirements may be nearly twice as high due to lower absorption of non-heme iron; consider higher supplementation doses 4.

Women with Hypothyroidism

Untreated hypothyroidism combined with iron deficiency increases risk of congenital cretinism (growth failure, mental retardation, neuropsychologic defects) 3. Treat hypothyroidism with levothyroxine adjusted to normalize TSH, checking levels every trimester 3.

Prevention Strategy

All pregnant women should receive routine iron and folic acid supplementation during pregnancy, either alone or as components of multiple micronutrient supplements 6.

Monitoring and Follow-Up

• Recheck hemoglobin/hematocrit 4 weeks after initiating treatment 3, 4
• Continue monitoring throughout pregnancy 3
• Screen at 4-6 weeks postpartum in women at risk for persistent anemia 3, 4
• Continue iron supplementation throughout pregnancy and postpartum period to prevent recurrence 4

Critical Pitfalls to Avoid

Do not use IV iron as routine first-line therapy—oral iron remains the standard for prophylaxis and mild anemia 8.

Do not rely solely on hemoglobin/hematocrit to diagnose iron deficiency, as physiologic hemodilution makes these imprecise 1.

Do not delay referral for severe anemia (hemoglobin <9.0 g/dL or <7.0 g/dL) to a specialist experienced in pregnancy anemia management 3, 4.

Do not forget postpartum screening in women who had anemia during pregnancy, as maternal anemia increases transfusion risk at delivery and can persist postpartum 3, 2.