The risk of hemorrhage is inversely related to the platelet count with the greatest risk when the platelet count is below 100,000 μL−1.The recurrence of NAIT has been estimated to be more than 80% in subsequent pregnancies in which the fetus also carries the target platelet antigen. Subsequent cases of NAIT may be equivalent or more severe.The fetal response to NAIT is variable and may include compensatory extramedullary hematopoiesis. Rarely, fetal hydrops may develop. Fetal anemia (in presence of red cell incompatibility) may also occur. Diagnosis
Doctors may consider a diagnosis of NAIT if they notice bleeding or bruising in a baby, or low platelet counts on a blood test after birth, or neurologic symptoms. Some babies may have a specific pinpoint rash called “petechiae”. If a diagnosis of NAIT is suspected, then the baby should be treated as if it had NAIT until the diagnosis is confirmed.The diagnosis is confirmed by taking blood samples from the babys parents, and sometimes the baby. Maternal and paternal platelet antigen phenotyping and screening of the maternal serum for anti-platelet antibodies can be performed. Additionally, platelet antigen genotyping can be performed on the maternal and paternal blood to determine the exact nature of the incompatibility.Neonatal platelet counts on laboratory testing are typically under 20,000 μL−1. Higher counts may suggest a different diagnosis, such as maternal immune thrombocytopenic purpura.Even in mildly affected babies, it is important to fully investigate and diagnose the baby because the results can be critical for the effective management of any future pregnancies.
However, IVIG and platelet transfusions are also associated with harm and therefore should be avoided if they are not necessary.After a first affected pregnancy, if a mother has plans for a subsequent pregnancy, then the mother and father should be typed for platelet antigens and the mother screened for alloantibodies. Testing is available through reference laboratories (such as ARUP). DNA testing of the father can be used to determine zygosity of the involved antigen and therefore risk to future pregnancies (if homozygous for the antigen, all subsequent pregnancies will be affected, if heterozygous, there is an approximate 50% risk to each subsequent pregnancy). During subsequent pregnancies, the genotype of the fetus can also be determined using amniotic fluid analysis or maternal blood as early as 18 weeks gestation to definitively determine the risk to the fetus. References
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