Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 150

The diagnosis of FNAIT is first suspected based upon a qualifying history of a fetus or neonate with suspected or confirmed thrombocytopenia. This presentation can vary widely, ranging from asymptomatic mild thrombocytopenia to spontaneous intracranial hemorrhage (ICH) in the setting of profound thrombocytopenia. The detection of newborn petechiae or ecchymoses in the early hours after birth can be a first sign of thrombocytopenia and should prompt a neonatal platelet count and further investigation if abnormal. ICH is the most severe complication of FNAIT, occurring in about 10–20% of cases. The majority of ICH presentations have a prenatal origin and can result in perinatal death or survival with permanent neurological disability.

A suspected FNAIT diagnosis requires evaluation by parental blood testing, which includes HPA genotyping of both parents. Should a platelet antigen incompatibility be determined within a tested couple, further maternal testing for the presence of antigen‐specific anti‐HPA antibodies is performed to secure a FNAIT diagnosis. Paternal genotyping is also important to determine recurrence risk in a subsequent pregnancy for the same couple, which can be either 50% (paternal heterozygosity) or 100% (paternal homozygosity) for a given disease‐causing HPA antigen, depending on paternal zygosity status. In cases involving paternal heterozygosity, amniocentesis can be performed to determine if the pregnancy is at risk. Chorionic villus sampling (CVS) is discouraged in pregnancies at risk for FNAIT, as it may exacerbate alloimmunization and increase risk for fetal loss. Cell‐free fetal DNA is a promising approach for the noninvasive determination of fetal HPA‐1a status, with limited data supporting clinical accuracy. However, in the United States access to this technology for that indication remains limited, and further validation may be required.

It should be noted that an inability to detect platelet‐specific antibodies does not entirely exclude a FNAIT diagnosis. One example includes cases in which months have elapsed after an affected delivery. For these patients, repeat maternal antibody screening may be considered on an every‐trimester basis in a subsequent at‐risk pregnancy.

Fetal and neonatal alloimmune thrombocytopenia testing is recommended if a patient has an obstetric history diagnostic or suggestive of FNAIT, such as a fetal or neonatal ICH or evidence of neonatal thrombocytopenia <50 000/mL³, regardless of the presumed etiology. Additionally, testing is advisable if a patient has a biological sister with history diagnostic or suggestive of FNAIT. Universal screening for HPA‐1a antibodies is not believed to be a cost‐effective strategy and is not recommended.

Differential diagnosis involves other conditions that might cause fetal or neonatal thrombocytopenia such as idiopathic thrombocytopenic purpura (ITP), which is also an IgG‐mediated phenomenon causing maternal thrombocytopenia and, occasionally, fetal or neonatal thrombocytopenia. ITP is infrequently associated with minor clinical bleeding in the newborn, and rarely causes fetal or intracranial hemorrhage. ITP clinically differs from FNAIT, as in the latter case the mother herself is usually healthy, with a normal platelet count. Other conditions associated with fetal or neonatal thrombocytopenia include but are not limited to selected maternal‐fetal infections (such as cytomegalovirus or parvovirus), congenital and inherited thrombocytopenias, rare instances of red blood cell antigen alloimmunization, severe ABO incompatibility, and disseminated intravascular coagulation.