Anemias in Pregnancy
With normal pregnancy, blood volume increases, which results in a concomitant hemodilution. Although red blood cell (RBC) mass increases during pregnancy, plasma volume increases more, resulting in a relative anemia. This results in a physiologically lowered hemoglobin (Hb) level, hematocrit (Hct) value, and RBC count, but it has no effect on the mean corpuscular volume (MCV). In an iron-replete population, anemia defined as a value less than the fifth percentile is a hemoglobin level of 11 g/dL or less in the first trimester, 10.5 g/dL or less in the second trimester, and 11 g/dL or less in the third trimester.
Many centers define anemia in a patient who is pregnant as an Hb value lower than 10.5 g/dL, as opposed to the reference range of 14 g/dL in a patient who is not pregnant. Treatment with 1 mg folic acid and daily iron is helpful when deficiencies are noted.
The simplest approach to the differential diagnoses of anemia is to differentiate anemias by the mean corpuscular volume (MCV), measured in fL.
MCV less than 80 fL or microcytic anemia etiologies are as follows:
Anemia of chronic disease
Anemia associated with copper deficiency
Anemia associated with lead poisoning
MCV 80-100 fL or normocytic anemia etiologies are as follows:
Early iron deficiency anemia
Anemia of chronic disease
Anemia associated with bone marrow suppression
Anemia associated with chronic renal insufficiency
Anemia associated with endocrine dysfunction
Autoimmune hemolytic anemia
Anemia associated with hypothyroidism or hypopituitarism
Hemolytic anemia associated with paroxysmal nocturnal hemoglobinuria
MCV greater than 100 fL or macrocytic anemia etiologies are as follows:
Folic acid deficiency anemia
Vitamin B-12–deficiency anemia
Drug-induced hemolytic anemia (eg, zidovudine)
Anemia associated with reticulocytosis
Anemia associated with liver disease
Anemia associated with ethanol abuse
Anemia associated with acute myelodysplastic syndrome
Iron deficiency anemia
Iron deficiency anemia accounts for 75-95% of the cases of anemia in pregnant women. A woman who is pregnant often has insufficient iron stores to meet the demands of pregnancy. Pregnant women are encouraged to supplement their diet with 60 mg of elemental iron daily. An MCV less than 80 mg/dL and hypochromia of the RBCs should prompt further studies, including total iron-binding capacity, ferritin levels, and Hb electrophoresis if iron deficiency is excluded.
Clinical symptoms of iron deficiency anemia include fatigue, headache, restless legs syndrome, and pica (in extreme situations). Treatment consists of additional supplementation with oral iron sulfate (320 mg, 1-3 times daily). Once-daily administration is preferable because more frequent iron supplementation can cause constipation.
The clinical consequences of iron deficiency anemia include preterm delivery, perinatal mortality, and postpartum depression. Fetal and neonatal consequences include low birth weight and poor mental and psychomotor performance.
Go to Iron Deficiency Anemia for complete information on this topic.
Folate and vitamin B-12 deficiency anemia
Folate deficiency is much less common than iron deficiency; however, taking 0.4 mg/d to reduce the risk of neural tube defects is recommended to all women contemplating pregnancy. Patients with a history of a prior fetus with a neural tube defect should take 4 mg/d. An increased MCV (typically >100 fL) can be suggestive of folate and/or B-12 vitamin deficiency; in this case, determine serum levels of vitamin B-12 and folate. If the levels are low, the patient may require oral folate at a dose of 1 mg 3 times daily.
Patients with vitamin B-12 deficiency need further workup to determine the level of intrinsic factor to exclude pernicious anemia. The Schilling test is not recommended during pregnancy, because of the radionuclide used in testing. Treatment of vitamin B-12 deficiency includes 0.1 mg/d for 1 week, followed by 6 weeks of continued therapy to reach a total administration of 2 mg.
Go to Pernicious Anemia for complete information on this topic.
Infectious causes of anemia
Infectious cause of anemia are more common in nonindustrialized countries.
Anemia can be caused by infections such as parvovirus B-19, cytomegalovirus (CMV), HIV, hepatitis viruses, Epstein-Barr virus (EBV), malaria, babesiosis, bartonellosis, hookworm infestation, and Clostridium toxin. If the patient’s history suggests exposure to any of these infectious agents, appropriate laboratory studies should be performed.
Diamond-Blackfan anemia is a rare (7 per 1 million) autosomal dominant disorder of pure red cell aplasia necessitating life-long transfusion. Women who are contemplating or who are pregnant require the consultation and care of a hematologist in conjunction with a maternal-fetal medicine specialist. Concerns during pregnancy include maintaining adequate hemoglobin while decreasing the risk of fetal exposure to the iron chelating agent (deferoxamine) used during transfusions.