What is the target hemoglobin (Hgb) level in pregnancy?

Target Hemoglobin Levels in Pregnancy

The target hemoglobin level in pregnancy should be ≥11 g/dL in the first trimester and ≥10.5 g/dL in the second and third trimesters. 1

Normal Hemoglobin Changes During Pregnancy

• Pregnancy causes physiological changes in hemoglobin concentration due to increased plasma volume and hemodilution 2
• In iron-replete women, the 5th percentile for hemoglobin is approximately:
  • 110 g/L (11 g/dL) in the first trimester
  • 105 g/L (10.5 g/dL) in the second and third trimesters 3
• These values represent the lower limit of normal in women receiving adequate iron supplementation 3

Defining Anemia in Pregnancy

• Anemia is defined as hemoglobin <11 g/dL in the first trimester and <10.5 g/dL in the second and third trimesters 1
• Iron deficiency is the most common cause (approximately 75%) of anemia in pregnancy 2
• Screening is recommended with a complete blood count in the first trimester and again at 24-28 weeks gestation 1

Clinical Implications of Different Hemoglobin Levels

• Mild anemia (Hb 10.0-10.9 g/dL):

  • Generally well-tolerated with minimal adverse outcomes 4
  • May actually be associated with decreased risks of certain complications compared to no anemia 4
  • Should be treated with oral iron supplementation 1

• Moderate anemia (Hb 7.0-9.9 g/dL):

  • Associated with increased risks of placental abruption (aOR 1.98), preterm birth (aOR 1.18), and severe postpartum hemorrhage (aOR 3.53) 4
  • Requires further investigation beyond simple iron deficiency 1

• Severe anemia (Hb <7.0 g/dL):

  • Associated with significantly higher risks of maternal and fetal complications 4
  • Linked to increased risk of maternal shock (aOR 14.98), ICU admission (aOR 2.88), and stillbirth (aOR 1.86) 4
  • Hemoglobin levels <6 g/dL correlate with poor pregnancy outcomes including prematurity, spontaneous abortions, low birth weight, and fetal deaths 2

Special Considerations

For Sickle Cell Disease

• For pregnant women with sickle cell disease, target hemoglobin should be >7.0 g/dL 5
• If transfusions are needed, aim for HbS level of <50% 5

For Congenital Fibrinogen Disorders

• In women with afibrinogenemia and hypofibrinogenemia:
  • Target fibrinogen level of ≥1 g/L throughout pregnancy 5
  • Increase to ≥1.5 g/L in case of vaginal bleeding or during labor and delivery 5

For Diabetes in Pregnancy

• No specific hemoglobin targets different from non-diabetic pregnant women 5
• Focus on glycemic targets:
  • Fasting glucose <95 mg/dL
  • One-hour postprandial glucose <140 mg/dL
  • Two-hour postprandial glucose <120 mg/dL 5

Treatment Approach for Anemia in Pregnancy

• First-line treatment for iron deficiency anemia is oral iron supplementation 1
• For patients who cannot tolerate, absorb, or respond to oral iron, intravenous iron is preferred 1
• Monitoring hemoglobin levels throughout pregnancy is essential to ensure targets are maintained 3

Clinical Pitfalls to Avoid

• Do not confuse physiologic hemodilution of pregnancy with true anemia requiring treatment 6
• Values outside the normal range are associated with pregnancy complications and fetal growth restriction 6
• Avoid overdiagnosis of anemia by using trimester-specific cutoffs rather than non-pregnant reference ranges 3
• Recognize that mild anemia may not require aggressive intervention, while moderate to severe anemia demands prompt evaluation and treatment 4