Alloimmune Thrombocytopenia. Disparity between maternal and fetal platelet antigens can stimulate maternal production of antiplatelet antibodies. Such platelet alloimmunization can be severe, and its pathophysiology is identical to that caused by red cell antigens (Chap. 15, p. 307).
Also called thrombocythemia, thrombocytosis generally is deined as persistent platelet counts >450,000/�L. Common causes of seconday or reactive thrombocytosis are iron deficiency, infection, inflammatory diseases, and malignant tumors (Deutsch, 2013). Platelet counts seldom exceed 800,000/�L in these secondary disorders, and prognosis depends on the underlying disease. On the other hand, primary or essential thrombocytosis accounts for most cases in which platelet counts exceed 1 millionl �L. It is a clonal disorder frequently due to an acquired mutation in the fAQ gene (Konkle, 2015). Thrombocytosis usually is asymptomatic, but arterial and venous thromboses may develop, and thrombosis is associated with pregnancy complications (Rabinerson, 2007; Randi, 2014). hese cases must be diferentiated from the sticky platelet syndrome, which is also associated with thromboses (Rac, 2011).
Normal pregnancies have been described in women whose mean platelet counts werer> 1.25 million/�L (Beard, 1991; Randi, 1994). Others report more adverse outcomes. Niittyvuopio and associates (2004) described 40 pregnancies in 16 women with essential thrombocythemia. Almost half had a spontaneous abortion, fetal demise, or preeclampsia. In 63 pregnancies in 36 women cared for at the Mayo Clinic, a third had a spontaneous miscarriage, but other pregnancy complications were uncommon (Gangat, 2009). In this observational study, aspirin therapy was associated with a signiicantly lower abortion rate than that in untreated women-1 versus 75 percent, respectively.
Suggested treatments during pregnancy include aspmn, low-molecular-weight heparin, and interferon-a (Finazzi, 2012). Interferon-a therapy during pregnancy was successful in 11 women in the review by Delage and coworkers (1996). One of these women had transient blindness at midpregnancy when her platelet count was 2.3 million/�L.
Although not a primary platelet disorder, some degree of thrombocytopenia accompanies the thrombotic microangiopathies, which include thrombotic thrombocytopenic purpura (TTP) and hemoytic uremic syndrome (HUS). hese syndromes have an incidence of2 to 6 per million persons per year (Miller, 2004). heir similarities to HELLP syndrome allude to their obstetrical ramiications (George, 2014).
Although diferent causes account for the variable findings within these syndromes, clinically, they frequently are indistinguishable. Most cases of TTP are thought to be caused by antibodies to or a plasma deficiency of ADAMTS13 (Ganesan, 201r1; Sadler, 2010). his endothelium-derived protease cleaves von Willebrand factor (vWF) to decrease its activity. Conversely, HUS is usually due to endothelial damage incited by viral or bacterial infections and is seen primarily in children (Ardissino, 2013; George, 2014).