Because 3-thalassemia major is caused by numerous mutations, prenatal diagnosis is diicult. For a given individual, targeted mutation analysis is done that requires prior identification of the familial mutation. The analysis is done using chorionic villus sampling and other techniques discussed in Chapter 14 (p. 293). Noninvasive testing of circulating fetal nucleic acids in maternal plasma for the diagnosis of 3-thalassemia has been described (Leung, 2012; Xiong, 2015).
Platelet abnormalities may precede pregnancy, develop during pregnancy coincidentally, or be induced by pregnancy. hrombocytopenia-deined by a platelet count < 150,000/�L-is identified in nearly 10 percent of gravidas (American College of Obstetricians and Gynecologists, 2016c). Of these cases, 75 percent are gestational thrombocytopenia, whereas 25 percent are due to other various causes. One other common cause is HELLP syndrome. Thrombocytopenia may be inherited or idiopathic, acute or chronic, and primary or associated with other disorders. Examples are shown in Table 56-5.
Burrows and Kelton (1993) reported that 6.6 percent of 15,471 pregnant women had a platelet count < 150,000/�L, and in 1.2 percent, it was <100,000/�L. hey further noted that almost 75 percent of 1027 women whose platelet counts were < 150,000/�L were found to have normal-variant incidental thrombocytopenia. Of the remainder, 21 percent had a hypertensive disorder of pregnancy, and 4 percent had an immunological disorder. A platelet count of <80,000/�L should trigger
TABLE 56-5. Some Causes of Thrombocytopenia in Pregnancy
APAS = antiphospholipid antibody syndrome; DIC = disseminated intravascular coagulopathy; HELLP = hemolysis, elevated liver enzyme levels, low platelet count;
MTP = massive transfusion protocol. Data from American College of Obstetrics and Gynecologists, 2016c; Aster, 2007; Diz-Ku:ukkaya, 2016.
an evaluation for etiologies other than incidental or gestational thrombocytopenia, which is unlikely to have a platelet count <50,000/�L (Gernsheimer, 2013).
he physiological decline in platelet concentration seen with gestational thrombocytopenia is usually evident in the third trimester and is thought to be predominantly due to hemodilution. The normal increased splenic mass characteristic of pregnancy may also be contributory (Maymon, 2006). Most evidence shows that platelet life span is unchanged in normal pregnancy (Kenny, 2015).
Benard-Soulier yndrome is characterized by lack of platelet membrane glycoprotein (GPIb/IX) and causes severe dysunction. Moreover, women exposed to fetal platelets carrying this glycoprotein can develop antibodies against this fetal GPIb/IX antigen to cause lloimmune fetal thrombocytopenia (Fujimori, 1999; Peng, 1991). A systematic review of 30 pregnancies in 18 women reported a 33-percent rate of primary postpartum hemorrhage, and half of women with bleeding required blood transfusion (Peitsidis, 2010). he reviewers also described six cases of neonatal lloimmune thrombocytopenia and two perinatl deaths. Close monitoring throughout pregnancy and 6 weeks postpartum is critical due to the possibility of life-threatening hemorrhage (Prabu, 2006).