Other conditions causing a low platelet count
Other conditions that can cause a low platelet count in the neonate include bacterial and viral infection, disseminated intravascular coagulation and other rare congenital conditions associated with a low platelet count. Pathophysiology
Platelets have many proteins on their surface. Each person has a different set of proteins, which are inherited from their parents. These different platelet proteins make different platelet groups, just like different proteins on red blood cells make different blood groups. These differences do not affect how the platelets work. However, if a baby inherits a protein that is found on the fathers platelets but is absent from the mothers platelets, the mother may respond to this foreign protein by developing an antibody that fights against it.This antibody may pass from the mothers blood into the babys blood and attach to the babys platelets. This antibody destroys the babys platelets and suppresses production of fetal platelets, they are also thought to weaken the blood vessel walls (vascular integrity) and affect production of new blood vessels (angiogenesis). This results in an increased risk of bleeding for the baby, and this can lead to the babys death. The mothers antibodies can remain in the babys bloodstream for weeks, and bleeding can occur in the baby before birth (fetal), during birth or after birth (neonatal).A number of different proteins can cause NAIT, about 80% of cases are caused by antibodies against platelet antigen HPA-1a, 15% by anti-HPA-5b, and 5% by other antibodies (e.g. HPA-1b, HPA-15, HPA-3 and HPA-9b).
The most common treatment is weekly IVIG infusions at a dosage of 1 g/kg beginning at 12 to 16 weeks of pregnancy in women who have had a previously affected child with an intracranial hemorrhage. For all other pregnancies, use of IVIG should be discussed, and, if indicated, should be started before 24 weeks of pregnancy and continued until the birth of the child. In some cases this dosage is increased to 2 g/kg and/or combined with a course of prednisolone  depending on the exact circumstances of the case.In a review they found that giving IVIG alone during pregnancy prevented intracranial hemorrhage in 98.7% of treated pregnancies (4 cases occurred in 315 pregnancies). This is a similar estimate to a previous review that only assessed the evidence within randomised controlled trials. They also found no consistent benefit of adding steroids to IVIG.The goal of both IVIG and platelet transfusion is to avoid hemorrhage. Ultrasound monitoring to detect hemorrhage in the fetus is not recommended as detection of intracranial hemorrhage generally indicates permanent brain damage (there is no intervention that can be performed to reverse the damage once it has occurred).Before delivery, the fetal platelet count may not be known, due to the high risks associated with cordocentesis (see above). If the platelet count is not known then assisted forms of delivery, for example forceps or ventouse, should be avoided to reduce the risk of harm.