Anemia in pregnancy

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Physiology & Definition - The Dilution Effect

  • Pregnancy causes a greater expansion of plasma volume (↑ ~50%) compared to red blood cell (RBC) mass (↑ ~25-30%).

  • This disproportionate increase results in hemodilution, a physiologic decrease in hemoglobin (Hb) and hematocrit (Hct).

  • Anemia Thresholds (CDC):

    • 1st Trimester: Hb < 11 g/dL
    • 2nd Trimester: Hb < 10.5 g/dL
    • 3rd Trimester: Hb < 11 g/dL

⭐ The nadir of physiologic anemia occurs in the late second trimester, coinciding with peak plasma volume.

Physiologic Changes in Pregnancy

Etiology & Diagnosis - Finding the Cause

  • Initial Workup: Start with a Complete Blood Count (CBC).
    • Anemia: Hemoglobin <11 g/dL (1st/3rd trimester) or <10.5 g/dL (2nd trimester).
  • Classification by MCV:
    • Microcytic (MCV <80 fL): Most common type.
      • Iron Deficiency Anemia (IDA): Check iron studies (↓ Ferritin, ↑ TIBC).
      • Thalassemia: Hemoglobin electrophoresis.
    • Normocytic (MCV 80-100 fL):
      • Physiologic hemodilution, anemia of chronic disease.
    • Macrocytic (MCV >100 fL):
      • Folate or Vitamin B12 deficiency.

⭐ Serum ferritin is the most sensitive and specific test for iron deficiency in pregnancy; a level <30 ng/mL is diagnostic.

Peripheral blood smear: microcytic hypochromic anemia

Screening & Workup - The Rightful Algorithm

  • Universal Screening: CBC at the initial prenatal visit & repeated at 24-28 weeks.
  • Anemia Thresholds:
    • 1st & 3rd Trimesters: Hb < 11 g/dL
    • 2nd Trimester: Hb < 10.5 g/dL

Peripheral blood smear: microcytic, hypochromic RBCs

High-Yield: Serum ferritin is the most sensitive and specific test for iron deficiency. A level < 30 ng/mL confirms iron deficiency anemia in pregnancy.

Management - Boosting the Blood

  • Iron Deficiency Anemia (IDA):
    • First-line: Oral ferrous sulfate (325 mg daily).
    • Take with Vitamin C to ↑ absorption.
    • IV iron for malabsorption, PO intolerance, or severe anemia near term.
  • Folate/B12 Deficiency: Replete the deficient vitamin.
  • Packed RBC Transfusion: For Hgb < 7 g/dL, hemodynamic instability, or acute hemorrhage.

⭐ Fetal iron uptake is preserved even in severe maternal deficiency; the fetus effectively acts as an iron parasite.

Complications - Risks for Two

  • Maternal Risks:
    • Impaired cardiac function → high-output failure (if Hb < 6 g/dL)
    • Preeclampsia
    • ↑ Postpartum hemorrhage (PPH) & infection risk
    • Poor tolerance to blood loss at delivery
  • Fetal & Neonatal Risks:
    • Low birth weight (LBW) & IUGR
    • Preterm delivery
    • Intrauterine fetal demise (IUFD)
    • Lower iron stores → neonatal anemia

⭐ Maternal iron deficiency anemia, especially in the first two trimesters, is associated with an increased risk of autism spectrum disorder, ADHD, and intellectual disability in the child.

Fetus, red blood cells, and iron supplements

High‑Yield Points - ⚡ Biggest Takeaways

  • Physiologic anemia of pregnancy is the most common type, resulting from hemodilution (plasma volume ↑ > RBC mass ↑).
  • Iron deficiency is the most common pathologic cause; screen with a CBC at the first prenatal visit and again at 24-28 weeks.
  • Diagnostic thresholds: Hb <11 g/dL in the 1st/3rd trimesters, and <10.5 g/dL in the 2nd.
  • Low serum ferritin is the most sensitive and specific test for iron deficiency.
  • Treat with oral ferrous sulfate; parenteral iron is reserved for severe cases or malabsorption.
  • Folate deficiency causes megaloblastic anemia and increases the risk of neural tube defects.

Practice Questions: Anemia in pregnancy

Test your understanding with these related questions

A 61-year-old woman presents for a routine health visit. She complains of generalized fatigue and lethargy on most days of the week for the past 4 months. She has no significant past medical history and is not taking any medications. She denies any history of smoking or recreational drug use but states that she drinks "socially" approx. 6 nights a week. She says she also enjoys a "nightcap," which is 1–2 glasses of wine before bed every night. The patient is afebrile, and her vital signs are within normal limits. On physical examination, there is significant pallor of the mucous membranes. Laboratory findings are significant for a mean corpuscular volume (MCV) of 72 fL, leukocyte count of 4,800/mL, hemoglobin of 11.0 g/dL, and platelet count of 611,000/mL. Stool guaiac test is negative. She is started on oral ferrous sulfate supplements. On follow-up, her laboratory parameters show no interval change in her MCV or platelet level, and she reports good compliance with the medication. Which of the following is the best next step in the management of this patient?

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Flashcards: Anemia in pregnancy

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How does blood pressure change during early pregnancy?_____

TAP TO REVEAL ANSWER

How does blood pressure change during early pregnancy?_____

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