Maternal Physiologic Changes With Pregnancy

Several normal adaptive changes occur in the hemato-logic environment during pregnancy. Plasma volume increases by about 50% with only a 20-50% rise in red cell mass, resulting in a normocytic anemia.6 Inadequate hematopoiesis can result if iron and folate stores are not supplemented in advance. The normocytic anemia often becomes microcytic if iron metabolism cannot keep pace with fetal demand despite supplementation.

Leukocytosis occurs during pregnancy, most likely due to increased levels of endogenous steroids. By the third trimester, white blood cell (WBC) may reach as high as 12,000/^L and up to 20,000-30,000/^L during labor.7 Platelet counts in the low normal range may be seen during gestation (gestational thrombocytopenia).6 Immune thrombocytopenic purpura occurs more often in young women; any platelet count that acutely drops or is less than 50,000/ ^L must be investigated.

The physiologic changes occurring with pregnancy can directly affect the dosing and toxicity of chemotherapeutic agents. The increase in renal blood flow, glomerular filtration rate, and creatinine clearance may increase the clearance of drugs excreted by the kidneys. Amniotic fluid may act as a physiologic third space, and thereby may enhance the toxicity of agents by delaying elimination. The physiologic increase in body water with the increase in plasma volume may change the volume of drug distribution.


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