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Anemia During Pregnancy


Lara A. Friel

, MD, PhD, University of Texas Health Medical School at Houston, McGovern Medical School

Last full review/revision Jun 2021| Content last modified Jun 2021

Anemia occurs in up to one third of women during the 3rd trimester. The most common causes of anemia are

(See also Anemia.)

If women have a hereditary anemia (such as sickle cell disease, hemoglobin S-C disease, or some thalassemias), the risk of problems is increased during pregnancy. If women are at increased risk of having any of these disorders because of race, ethnic background, or family history, blood tests to check for the disorders are routinely done before delivery. Chorionic villus sampling or amniocentesis may be done to check for these disorders in the fetus.

Symptoms of Anemia During Pregnancy

When anemia develops, the blood cannot carry as much oxygen as it normally does. At first, anemia causes no symptoms or only vague symptoms, such as fatigue, weakness, and light-headedness. Affected women may look pale. If anemia is severe, the pulse may be rapid and weak, women may faint, and blood pressure may be low.

If anemia persists, the following may result:

  • The fetus may not receive enough oxygen, which is needed for normal growth and development, especially of the brain.
  • Pregnant women may become excessively tired and short of breath.
  • The risk of preterm labor is increased.
  • After delivery, the risk of infection in the woman is increased.

The bleeding that normally occurs during labor and delivery can dangerously worsen anemia in these women.

Diagnosis of Anemia During Pregnancy

  • Blood tests

Anemia is usually detected when doctors do a routine complete blood count at the first examination after pregnancy is confirmed.

Treatment of Anemia During Pregnancy

  • Treatment of the anemia
  • For severe symptoms or certain problems in the fetus, transfusions

Measures to correct anemia during pregnancy depend on the cause (see below).

Whether blood transfusions are needed depends on whether the following occur:

  • Symptoms, such as light-headedness, weakness, and fatigue, are severe.
  • Anemia affects breathing or the heart rate.
  • The heart rate pattern in the fetus is abnormal.

Anemia Due to Iron or Folate Deficiency

Iron deficiency is the cause of anemia during pregnancy in about 95% of cases. Iron deficiency anemia is usually caused by

  • Not consuming enough iron in the diet (especially in adolescent girls)
  • Menstruating
  • Having had a previous pregnancy

Women normally and regularly lose iron every month during menstruation. The amount of iron lost during menstruation is about the same as the amount women normally consume each month. Thus, women cannot store much iron.

To make red blood cells in the fetus, pregnant women need twice as much iron as usual. As a result, iron deficiency commonly develops, and anemia often results.

Folate (folic acid) deficiency may also cause anemia during pregnancy. If folate is deficient, the risk of having a baby with a birth defect of the brain or spinal cord (neural tube defect), such as spina bifida, is increased.

Blood tests can confirm the diagnosis of iron deficiency anemia or folate deficiency anemia.

Anemia can usually be prevented or treated by taking iron and folate supplements during pregnancy. If a pregnant woman has iron deficiency, the newborn is usually given iron supplements. Taking folate supplements before becoming pregnant and during pregnancy reduces the risk of the baby having a neural tube defect.

Sickle Cell Disease

In addition to causing symptoms of anemia, sickle cell disease increases the risk of the following during pregnancy:

A sudden, severe attack of pain, called sickle cell crisis, may occur during pregnancy as at any other time. The more severe that sickle cell disease is before pregnancy, the higher the risk of health problems for pregnant women and the fetus, and the higher the risk of death for the fetus during pregnancy. Sickle cell anemia almost always worsens as pregnancy progresses.

If given regular blood transfusions, women with sickle cell disease are less likely to have sickle cell crises, but they become more likely to reject the transfused blood. This condition, called alloimmunization, can be life threatening. Also, transfusions to pregnant women do not reduce risks for the fetus. Thus, transfusions are used only if one of the following occurs:

  • The anemia causes symptoms, heart failure, or a severe bacterial infection.
  • Serious problems, such as bleeding or an infection of the blood (sepsis), develop during labor and delivery.

If a sickle cell crisis occurs, women are treated as they would be if they were not pregnant. They are hospitalized and given fluids intravenously, oxygen, and drugs to relieve pain. If the anemia is severe, they are given a blood transfusion.

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