Normal pregnancy is characterized by profound changes in almost every organ system to accommodate the demands of the fetoplacental unit. The hematologic system must adapt in a number of ways, such as provision of vitamins and minerals for fetal hematopoiesis (iron, vitamin B12, folic acid), which can exacerbate maternal anemia, and preparation for bleeding at delivery, which requires enhanced hemostatic function.
While these changes facilitate healthy pregnancy, they also increase the risks of some conditions (eg, venous thromboembolism). In addition, physiologic changes in blood cell counts must be distinguished from pregnancy complications that require specific treatments.
This topic discusses physiologic changes in blood cells and hemostasis during pregnancy. Hematologic complications of pregnancy are discussed in separate topic reviews.
The most significant hematological changes during pregnancy include the following (table 1):