Fetal and neonatal thrombocytopenia (NNT) may lead to bleeding and to death or neurological sequelae. NNT affects 25-40% of the infants in intensive care units and even in the absence of bleeding, must be considered as a potentially valuable sign. There are various causes, the main one being bacterial or viral infection, followed by immune thrombocytopenia which may be due to maternal autoantibodies or alloantibodies that cross the placenta. Management during pregnancy aims to prevent fetal bleeding especially in the central nervous system, and to avoid birth trauma. Percutaneous umbilical blood sampling provides a direct measure of the fetal platelet count and makes it possible to assess the effectiveness of therapy. Other causes, such as disseminated intravascular coagulation, local platelet consumption or antenatal hypoxia, must also be considered. Finally, the accuracy of the diagnosis of the mechanism of NNT will determine the specific management for the mother, the newborn and any subsequent pregnancy.