Anemia During Pregnancy

Classification and Diagnosis

• The American College of Obstetricians and Gynecologists defines anemia during pregnancy as a hemoglobin level less than 10.5 g/dL in the second or third trimester 1
• Anemia can be classified as mild, moderate, or severe based on hemoglobin levels, with mild anemia having a hemoglobin level between 10.0-10.9 g/dL in the first trimestre or 10.0-10.4 g/dL in the second or third trimestre, moderate anemia having a hemoglobin level between 7.0-9.9 g/dL, and severe anemia having a hemoglobin level less than 7.0 g/dL 2, 3
• Anemia can also be classified based on the concentration of hemoglobin expressed as multiples of the median (MoM) for gestational age, with mild anemia having a MoM of 0.83-0.65, moderate anemia having a MoM of 0.64-0.55, and severe anemia having a MoM less than 0.55 2, 3

Reference Values During Pregnancy

• Normal hemoglobin values increase with gestational age, and anemia is diagnosed when the hemoglobin value is more than 2 standard deviations below the mean 2
• The median hemoglobin values for fetuses at different gestational ages are: 10.6 g/dL at 18 weeks, 12.6 g/dL at 28 weeks, and 13.5 g/dL at 37 weeks, with severe anemia defined as a hemoglobin level less than 5.8 g/dL at 18 weeks, less than 6.9 g/dL at 28 weeks, and less than 7.5 g/dL at 37 weeks 4

Physiological Changes During Pregnancy

• During the first and second trimesters, hemoglobin and hematocrit decrease due to blood volume expansion, but with adequate iron intake, hemoglobin and hematocrit increase gradually towards pre-pregnancy levels in the third trimester 5
• Altitude, smoking, and ethnicity can affect hemoglobin values, with residence at high altitudes, smoking, and certain ethnicities causing an increase in hemoglobin values 5

Clinical Implications

• Severe fetal anemia can lead to hydrops fetalis and fetal death 2, 3
• The Centers for Disease Control and Prevention recommends initiating oral iron supplements at a low dose (30 mg/day) from the first prenatal visit, and promoting the consumption of iron-rich foods and foods that enhance iron absorption 6

Management of Anemia During Pregnancy

• The American College of Obstetricians and Gynecologists recommends a therapeutic trial of oral iron (60-120 mg/day) for mild anemia, and evaluation and possible referral to a specialist for moderate to severe anemia 6
• If anemia does not respond to iron treatment after 4 weeks, further evaluation with other parameters such as MCV, RDW, and serum ferritin should be performed 6
• When hemoglobin normalizes for the stage of gestation, the iron dose can be decreased to 30 mg/day 6

Management of Severe Anemia in Early Pregnancy

Immediate Management

• Urgent blood transfusion is the first-line treatment for hemoglobin levels below 7.0 g/dL in pregnancy to prevent hemodynamic compromise 7
• For hemoglobin levels <7.5 g/dL, packed red cell transfusion is indicated, especially when there are clinical symptoms or no response to other therapeutic measures 7
• Typically, transfusion of 2-3 units of packed red blood cells is recommended to address the acute episode, with each unit expected to raise hemoglobin by approximately 1.5 g/dL 7

Post-Transfusion Management

• After initial stabilization with blood transfusion, oral iron supplementation should be initiated at 60-120 mg/day, as recommended by the Centers for Disease Control and Prevention 8
• Monitor hemoglobin levels closely following transfusion to ensure adequate response 8
• Investigate underlying causes of severe anemia through additional laboratory testing including mean corpuscular volume, red cell distribution width, and serum ferritin 8

Follow-up Care

• After initial correction of severe anemia, continue iron supplementation throughout pregnancy, as recommended by the Centers for Disease Control and Prevention 8
• Schedule follow-up hemoglobin testing within 1-2 weeks after transfusion 8
• Once hemoglobin normalizes for gestational age, decrease iron supplementation to maintenance dose of 30 mg/day 8
• Provide nutritional counseling regarding iron-rich foods and absorption enhancers 8

Management of Severe Maternal Anemia

Immediate Management

• Establish IV access immediately and prepare for potential emergency delivery if fetal distress develops, according to the American College of Obstetricians and Gynecologists 9
• Perform transfusion in a location with immediate access to operating room capabilities given the viable gestational age, as recommended by the American College of Obstetricians and Gynecologists 9

Critical Monitoring During Transfusion

• Continuous maternal vital signs and fetal heart rate monitoring throughout transfusion should be performed, as recommended by the American College of Obstetricians and Gynecologists 9

Post-Transfusion Evaluation

• Hemoglobin electrophoresis should be performed if the patient is of African, Mediterranean, or Southeast Asian ancestry to rule out thalassemia or hemoglobinopathy, according to the Centers for Disease Control and Prevention 10
• A peripheral blood smear should be conducted to investigate the underlying cause of anemia, as recommended by the American College of Obstetricians and Gynecologists 9

Iron Supplementation

• Initiate oral iron therapy at 60-120 mg elemental iron daily immediately after transfusion, as recommended by the Centers for Disease Control and Prevention 10
• Continue this therapeutic dose throughout pregnancy, and monitor hemoglobin response within 1-2 weeks, expecting an increase of at least 1 g/dL after 4 weeks of treatment, according to the Centers for Disease Control and Prevention 10

Obstetric Management Considerations

• Administer corticosteroids for fetal lung maturity given the viable gestational age and potential need for preterm delivery, as recommended by the American College of Obstetricians and Gynecologists 9, 11
• Plan delivery timing, taking into account the severity of maternal anemia and the need for potential preterm delivery, according to the American College of Obstetricians and Gynecologists 9, 11

Nutritional Counseling

• Counsel patients on iron-rich foods, absorption enhancers, and avoidance of iron absorption inhibitors, as recommended by the Centers for Disease Control and Prevention 10

Optimal Hemoglobin Levels in Pregnancy

Definition and Screening

• The American College of Obstetricians and Gynecologists recommends screening all pregnant women with a complete blood count at the first prenatal visit and again at 24-28 weeks of gestation 12
• The International Federation of Gynecology and Obstetrics (FIGO) recommends additional screening at 28 weeks to ensure detection of anemia that develops during the third trimester 12

Management and Treatment

• The Centers for Disease Control and Prevention (CDC) recommends routine iron supplementation starting at the first prenatal visit, with 30 mg/day of elemental iron to prevent iron deficiency anemia 13
• For mild anemia (≥10.0 g/dL), initiate therapeutic oral iron at 60-120 mg elemental iron daily, with intermittent iron dosing (every other day) being as effective as daily dosing with fewer gastrointestinal side effects 14

Critical Considerations

• The American Diabetes Association notes that A1C cutoffs or diabetes management guidelines should not be used to determine hemoglobin targets in pregnancy, as they address glycemic control, not hematologic parameters 13, 12, 14

Fetal Anemia Assessment and Management in Hemoglobinopathies

Normal Fetal Hemoglobin Reference Ranges

• In fetuses, the expected total hemoglobin concentration rises from approximately 10.6 g/dL at 18 weeks gestation to about 13.8 g/dL at 40 weeks; a measured value of 9.0 g/dL therefore falls below the normal range for any gestational age. [15][16]17

Severity Assessment of Fetal Anemia

• A fetal hemoglobin level of 9.0 g/dL corresponds to roughly 0.65–0.70 multiples of the median (MoM) for the appropriate gestational age, indicating moderate fetal anemia. [15][16]

Diagnostic Doppler Evaluation

• Middle‑cerebral‑artery (MCA) Doppler ultrasound should be performed with the sample volume placed as close as possible to the vessel origin and the transducer aligned at a zero‑degree angle; this technique reliably detects increased blood flow velocity associated with fetal anemia. [16][17]18

Etiology of Elevated Fetal HbF with Absent Adult HbA

• One possible cause of markedly elevated fetal hemoglobin (HbF) together with absent adult hemoglobin (HbA) in the fetus is homozygous α‑thalassemia (Hb Bart’s disease), which typically leads to hydrops fetalis and fetal demise. [15][17]

Management of Severe Fetal Anemia

• When MCA‑PSV exceeds 1.5 MoM, the fetus should be referred promptly to a tertiary center with expertise in intra‑uterine transfusion to mitigate the risks of severe anemia and its complications. [16][17]18