Effect of pregnancy on maternal physiology
Normal pregnancy involves many changes in maternal physiology including alterations in hematologic parameters. These changes include expansion in maternal blood and plasma volume. The increase in plasma volume is relatively larger than the increase in red cell mass resulting in a decrease in hemoglobin concentration. An increase in the levels of some plasma proteins alters the balance of coagulation and fibrinolysis.
Worldwide, the predominant cause of anemia in pregnancy is iron deficiency. Fetal requirements for iron are met despite maternal deficiency, but maternal iron deficiency has a number of adverse consequences including an increased frequency of preterm delivery and low-birth-weight infants.
Effect of Pregnancy on bleeding
Bleeding disorders in pregnancy are a common reason for hematologic consultation and evoke concern for both the mother and child. Life-threatening bleeding caused by disseminated intravascular coagulation is seen with some complications unique to pregnancy, including placental abruption, retained dead fetus, and amniotic fluid embolism. Von Willebrand disease is the commonest inherited bleeding disorder, but because of increases in factor VIII level and von Willebrand factor (VWF) during pregnancy, excessive bleeding at delivery is rarely a problem. Factor levels fall rapidly postpartum, and serious hemorrhage can occur during this period.
Carriers of hemophilia A and B should be monitored during pregnancy to determine if factor levels will be adequate for delivery at term. Caution should be exercised at delivery and during the first few days of life with offspring of hemophilia carriers until hemophilia testing is completed and the infant’s status is known. Acquired hemophilia as a result of factor VIII autoantibodies is rare, but can occur during pregnancy or the puerperium.
Thrombocytopenia is not uncommon in pregnancy, and its causes include several conditions that are unique to pregnancy, such as preeclampsia. Idiopathic thrombocytopenic purpura (ITP) is common, it is often exacerbated in pregnancy, and is managed conservatively if possible; close followup of newborns of mothers with ITP is essential. HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome and TTP (thrombotic thrombocytopenic purpura)/HUS (hemolytic uremic syndrome) are also seen in pregnancy and the puerperium. HELLP syndrome is managed with delivery if possible, whereas TTP requires plasma exchange. Inherited and acquired prothrombotic conditions can be exacerbated by pregnancy and can result in adverse reproductive outcomes as well as venous thromboembolism.
In general, the teratogenic effects of chemotherapy are greatest in the first trimester; however, care must be taken in later trimesters to avoid cytopenias of both mother and fetus at delivery. Hemorrhagic and thrombotic complications associated with pregnancy in females with essential thrombocythemia and polycythemia vera present a unique challenge due to the lack of controlled trials in these situations.