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Anemia During Pregnancy

By Lara A. Friel, MD, PhD, Associate Professor, Maternal-Fetal Medicine Division, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Texas Health Medical School at Houston, McGovern Medical School

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

  • Iron deficiency

  • Folate deficiency

If women have a hereditary anemia (such as sickle cell disease, hemoglobin S-C disease, and 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 are routinely done before delivery to check for the disorders. Chorionic villus sampling or amniocentesis may be done to check for these disorders in the fetus.

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.

The bleeding that normally occurs during labor and delivery can dangerously worsen anemia in these women. Also, infections are more likely to develop after delivery.

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

Anemia due to iron or folate deficiency

During pregnancy, anemia results from iron deficiency in about 95% of cases.

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.

Anemia may also develop during pregnancy because of a folate (folic acid) deficiency. 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.

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.

Sickle cell disease

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

  • Infections: Pneumonia, urinary tract infections, and infections of the uterus are the most common.

  • High blood pressure: About one third of pregnant women who have sickle cell disease develop high blood pressure during pregnancy.

  • Heart failure

  • Blockage of arteries in the lungs by blood clots (pulmonary embolism): This problem may be life threatening.

  • Problems in the fetus: The fetus may grow slowly or not as much as expected. The fetus may be born prematurely or even die.

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 the anemia causes symptoms, heart failure, or a severe bacterial infection or if 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.