Anemia develops in most pregnant women to some degree. The most common cause is an iron deficiency.

For women who 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 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.

Anemia due to nutritional deficiencies: During pregnancy, iron deficiency commonly develops because women need twice as much iron as usual to make red blood cells in the fetus. 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, such as spina bifida, is increased.

Anemia can usually be prevented or treated by taking iron and folate supplements during pregnancy. However, if anemia becomes severe and persists, the blood's capacity to carry oxygen is decreased, and 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 who have severe anemia may become excessively tired, short of breath, and light-headed.
• The risk of preterm labor is increased.

A normal amount of bleeding during labor and delivery can cause the anemia in these women to become dangerously severe. They are more likely to develop infections after delivery.

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 of 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 even die.

A sudden, severe attack of pain, called sickle cell crisis, may occur during pregnancy as at any other time. The more severe sickle cell disease was 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.

With regular blood transfusions, women 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.

Last full review/revision December 2008 by Sean C. Blackwell, MD