Anemia in Pregnancy

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)