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Pregnancy & Prenatal Testing

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Third Trimester: Complete Blood Count (CBC)

The complete blood count (CBC) is a test that evaluates the cells that circulate in blood. Blood consists of three types of cells suspended in fluid called plasma: red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). To identify and prevent problems, a CBC may be done before pregnancy, if possible, at the beginning of pregnancy, and one or more times during pregnancy. The first baseline results can be compared to later values to look for changes that could indicate a health issue.

  • Red blood cells contain hemoglobin, a protein that gives blood its red color. It binds to oxygen in your lungs, transports it throughout the body, and releases it to the cells and tissues. During pregnancy, a woman's hemoglobin must transport enough oxygen to meet both her and her fetus' needs. If a woman has insufficient RBCs and/or hemoglobin, she is said to be anemic.

    Many pregnant women will experience some degree of anemia. While mild anemia can make you feel tired and weak, more severe anemia in a pregnant woman can cause a fetus to receive too little oxygen to support normal development.

    All women lose a small amount of blood during delivery. Although this is usually not a problem, even a small amount of blood loss can be harmful to women with anemia. A healthcare practitioner may want to know the level of hemoglobin in a pregnant woman's blood before delivery to assess the possible impact of the expected blood loss.

  • White blood cells help protect the body from infections and also have other immune functions. Evaluating WBCs during a woman's pregnancy can help detect infections so that they may be treated and resolved before they cause significant health problems in the mother or her baby.
  • Platelets are special cell fragments in the blood that help form clots to stop bleeding. Women with low platelet counts, or who have platelets that don't function properly to form clots, are at risk of life-threatening bleeding during delivery. Follow-up testing may be needed to help determine treatment options if a platelet problem is detected.

March of Dimes: Pregnancy complications – Anemia