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Evaluation of Anemia in Pregnancy

7/1/2013 - Julie L. Hansen, MD

Editor:  Ronald T. Burkman, MD

Anemia is common in pregnancy because blood volume expands by approximately 50% in a singleton gestation while total red blood cell mass only increases about 25%. All pregnant patients should be screened for anemia at the first obstetrical visit and in the third trimester. Anemia in pregnancy is defined as a Hgb < 11 g/dL and Hct < 33% in the first and third trimesters, and Hgb < 10.5 g/dL and Hct < 32% in the second trimester.

Iron deficiency is the most common cause of anemia in pregnancy in the United States. Risk factors include low socio-economic status, multiple gestations, history of menorrhagia, short interval between pregnancies, and malnutrition or other dietary factors including malabsorption related to bariatric procedures. Other causes of anemia include hemoglobinopathies, G6PD deficiency, and chronic disease related to liver disease, thyroid disease, uremia, chronic infections, or malignancies.

Initial anemia evaluation should include medical history, physical examination, and measurements of the complete blood count and red blood cell indices. A peripheral smear is helpful for the diagnosis of hemolytic or parasitic disease. A hemoglobin electrophoresis is indicated for evaluation of thalassemia or sickle cell disease in populations with established risk including those from regions of Africa, the Middle East, the Mediterranean, Southeast Asia, Caribbean, South America, and the Western Pacific.

An MCV < 80 fL should be evaluated with a serum ferritin levels; other tests could include plasma iron level, plasma total-iron-binding capacity, transferrin saturation, and free erythrocyte protoporphyrin.  A low ferritin is diagnostic of iron deficiency anemia and the patient should be started on iron supplementation. A Hgb electrophoresis will determine if sickle cell disease (Hb AS, SC, SS, or SC) or other hemoglobinopathies (Hb C, D, or E) are present. A hemoglobin electrophoresis with a Hb A2 > 3.5% with a normal ferritin level is found in women with beta-thalassemia. A Hb A2 <3.5% is found in women with alpha-thalassemia, hemoglobin H disease, and chronic anemia. In both cases, the partner should be tested to assess carrier status, and the couple referred for genetic counseling if both are carriers of thalassemia or sickle cell disease.

When the MCV is ≥80 fL, a reticulocyte count should be performed. A low reticulocyte count with a normal MCV is suggestive of combined iron and folate deficiency, iron and B12 deficiency, or chronic disease anemia. A low reticulocyte count with an MCV ≥100 is consistent with folate or B12 deficiency, and serum levels of folate and B12 should be obtained. A high reticulocyte count suggests hemolysis and should prompt a peripheral smear, direct Coombs test, and hemoglobin electrophoresis. The hemolysis could be due to glucose-6-phosphate dehydrogenase (G6PD) deficiency or blood loss. A diagnosis of G6PD deficiency should be considered in women of Mediterranean, Asian, Middle Eastern, Hispanic, West Indies, and African descent. If blood loss is suspected based on history, a source of the loss must be identified.

Of note, severe anemia with maternal Hgb levels < 6 g/dL is associated with abnormal fetal oxygenation, nonreassuring fetal status, reduced amniotic fluid, fetal cerebral vasodilation, and fetal death. Maternal transfusion should be considered for fetal indications.

Further Reading:

Initial approval: July 2013; Revised September 2018

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This document is designed to aid practitioners in providing appropriate obstetric and gynecologic care. Recommendations are derived from major society guidelines and high quality evidence when available, supplemented by the opinion of the author and editorial board when necessary. It should not be construed as dictating an exclusive course of treatment or procedure to be followed.

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