This chapter describes the epidemiology, clinical diagnosis, and clinical significance of Fetal and neonatal alloimmune thrombocytopenia (FNAIT) in pregnancy. FNAIT is the commonest cause of severe neonatal thrombocytopenia, and is analogous to the fetal/neonatal anemia caused by hemolytic disease of the fetus and newborn (HDFN). FNAIT is usually suspected in neonates with bleeding or severe, unexplained, and/or isolated postnatal thrombocytopenia. The strategies for ante-natal treatment have included the use of serial platelet transfusions, which while effective are invasive and associated with significant morbidity and mortality. Significant recent progress has involved refinement of maternal treatment, stratifying it according to the likely severity of FNAIT based on the history in previous pregnancies. However, the ideal ante-natal treatment, which is effective without causing significant side-effects to the mother or fetus, has yet to be determined, and further clinical trials are needed.

Thrombocytopenia in the mother and fetus is a common problem. This chapter reviews its causes, clinical significance, investigation and management. Thrombocytopenia complicating hypertensive disorders of pregnancy is responsible for about 20% of cases of maternal thrombocytopenia. The pregnancy-related causes of disseminated intravascular coagulation (DIC) include pre-eclampsia, placental abruption, amniotic fluid embolism and, rarely, retention of a dead fetus. Immune thrombocytopenia is responsible for about 4% of maternal thrombocytopenia. Most cases are due to idiopathic autoimmune thrombocytopenia, but some are drug-related and some associated with HIV infection. Neonatal thrombocytopenia has many causes, and is the most common haematological problem in the newborn infant, and probably the fetus as well. A better understanding of the risks of thrombocytopenia in pregnancy to the mother and fetus has resulted in better targeting of treatment: withholding it in low-risk situations and using intensive therapy where there is high risk.