Anemia in Pregnancy

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Be sure to check out the new ACOG Practice Bulletin #233 on anemia — first time it’s been updated in a while! And while you’re at it, check out our old episode on sickle cell anemia.

Physiologic Changes in Pregnancy to Blood Volume 

  • Definitions

    • Remember that anemia in pregnancy is defined as: 

      • Hgb <11 g/dL in the first and third trimester 

      • Hgb <10.5 g/dL in the second trimester 

      • Previously, ACOG had discussed a lower threshold for certain people based on race, but one important study found that this lower threshold likely contributes to the perpetuation of racial disparities in medicine without a scientific reason for lower Hgb 

  • What happens in pregnancy? 

    • Physiologic

      • Plasma volume expands by 40-50%

      • Erythrocyte mass expands by 15-25% 

      • So even though there is increased red cell mass, it seems overall that HCT % goes down 

    • There is also increased iron requirement, so it is more likely for people to become iron deficient 

Causes of Anemia in Pregnancy 

  • Acquired 

    • Deficiency 

      • Iron deficiency - by far the most common 

      • B12 deficiency 

      • Folic acid deficiency 

    • Hemorrhagic 

    • Anemia of chronic disease 

    • Acquired hemolytic anemia 

    • Aplastic anemia 

  • Inherited 

    • Thalassemias 

    • Sickle cell 

    • Hemoglobinopathies 

    • Inherited hemolytic anemias 

Work-up of Anemia in Pregnancy 

  • Screening 

    • All pregnant people should be screened for anemia with CBC in the first trimester and again right before third trimester (usually 24-28 weeks) 

    • Also, should have discussion with everyone about screening for hemoglobinopathies if they have not been screened before 

  • Work up of asymptomatic with mild to moderate anemia: 

    • Anemia type: microcytic vs normocytic vs macrocytic 

      • Microcytic (MCV < 80 fl) 

        • Most commonly: iron deficiency 

        • But can also be caused by thalassemias, anemia of chronic disease, sideroblastic anemia, etc. 

      • Normocytic (MCV 80-100fL) 

        • Hemorrhagic or early iron deficiency = common 

        • Others: anemia of chronic disease, bone marrow suppression, chronic renal insufficiency, hemolytic anemia 

      • Macrocytic (MCV > 100 fL) 

        • Folic acid deficiency, B12 deficiency = most common 

        • Others: Reticulocytosis, liver disease, alcohol abuse, drug-induced hemolytic anemia 

  • Iron studies with measurement of red blood cell indices, serum iron levels, ferritin levels 

    • Some places also include a total iron-binding capacity 

    • In someone with iron deficiency, iron levels and ferritin will be low, while TIBC will be high 

  • Peripheral blood smear 

  • Can also look at vitamin B12 and folate levels if macrocytic 

  • Other work-up: 

    • If not responding to treatment with iron, folate, or B12, then further workup should be done 

    • Ie. is there a reason for malabsorption (gastric bypass?) 

    • Is there a reason for blood loss? 

Treatment of Anemia in Pregnancy 

  • Iron deficiency 

    • Can start with oral iron, unless there is a reason for malabsorption 

      • Usual requirements: 27 mg daily during pregnancy, and usual diet will live 15 mg of elemental iron/day 

      • Most oral forms of iron will exceed this 

      • If unable to tolerate oral iron or has reasons for malabsorption, can do IV iron, which can come in the form of iron dextran, ferric gluconate, or iron sucrose 

  • Folate or B12 deficiency

    •  MCV > 115 is almost exclusively seen in people with folate or B12 deficiency 

    • Give folate or B12! 

    • Folic acid: 400 mcg/day unless there are other indications for increased folate (ie. history of neural tube defect affecting child, on anti-epileptics) 

    • B12: usually only seen in people with gastric resection or Crohn disease 

      • Usually given IM every month, 1000 mcg/injection 

  • Other causes 

    • Depending on the cause, may need to work with colleagues from other specialties 

    • Or your friendly neighborhood MFM 

  • A word on transfusion 

    • Hgb <6 g/dL have been associated with abnormal fetal oxygenation 

    • Usually recommend transfusion if Hgb <7 or if symptomatic 

    • However, can consider higher threshold if other co-morbidites (ie. sickle cell anemia with known crises if Hgb <7)