Thrombocytopenia (TP) affects 7-10% of pregnant women. It occurs 4 times more frequently in pregnancy than in the non-pregnant women population. Women with thrombocytopenia in pregnancy are a heterogeneous and poorly known group. There are several possible causes of thrombocytopenia in pregnancy. The most common are: gestational thrombocytopenia (GE) (60-75%), preeclampsia (PE) and HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome associated TP (21%), and idiopathic immune thrombocytopenia (ITP) (3-10%). Although thrombocytopenia diagnosed in pregnancy in most cases has a mild course, it has also been reported to be associated with a higher rate of preterm birth and premature detachment of the placenta. Some cases of severe thrombocytopenia with systemic involvement are associated with high risk of serious perinatal complications and require early diagnosis, careful clinical monitoring and medical treatment. The differential diagnosis and proper assessment of clinical risk of TP during pregnancy may be of great concern. The article discusses these issues, focusing on pathophysiology of TP in pregnancy.