Auto- and alloimmune thrombocytopenias in pregnancy may seriously impact on both mother and fetus. Autoimmune thrombocytopenia (ITP) affects both mothers and fetuses but is considered to be quite benign for both groups. The 'facts' are that: 1) ITP occurs commonly in pregnancy; 2) there has been no reported maternal mortality in more than 20 years; 3) management, except at delivery, is similar to management in the non-pregnant state; 4) splenectomy is virtually never required during pregnancy; 5) significant neonatal thrombocytopenia occurs in approximately 10% of cases and intra-cranial hemorrhage (ICH) 1%; 6) the course of the first sibling predicts that of the next sibling; and 7) the fetal platelet count can be successfully determined (if desired) by either fetal blood sampling (FBS) or by fetal scalp sampling. Many other important considerations remain undetermined: 1) non-invasive prediction of severe fetal thrombocytopenia; 2) the appropriate mode of delivery for a thrombocytopenic fetus; 3) the role of anti-platelet antibody testing; and 4) the effects on the fetal platelet count of maternal therapy. Alloimmune thrombocytopenia (AIT) is easier to outline because it is a far more serious fetal disorder: 1) neonatal platelet counts < 20,000/microliter are common in AIT; 2) there is a 10-30% ICH rate in first affected newborns, some of which occur antenatally; 3) there is no universal prenatal screening although this would be scientifically feasible; 4) testing is complex and requires an experienced laboratory that can test at least five platelet antigens and has sufficient typed controls to confirm the specificity of any anti-platelet antibodies detected; 5) the second affected sibling in a family is usually more severely affected than the first; 6) treatment of the thrombocytopenic neonate can be accomplished with intravenous (i.v.) gammaglobulin and/or platelet transfusions; and 7) treatment of the fetal platelet count can be accomplished in most instances by infusing the mother with i.v. gammaglobulin with or without steroids; platelet transfusions to the fetus is another option.