Starting from their first description, antiphospholipid antibodies (aPL) were associated with repeated miscarriages and fetal losses. Other complications of pregnancy like preterm birth,with pre-eclampsia or severe placental insufficiency were also frequently reported and are included in the current classification criteria of the antiphospholipid syndrome (APS). The titre, the isotype of the antibodies or their antigen specificity may be important in the risk level determination. Some of the difference in the reported results can be explained by the poor standardization achieved in aPL testing or by the not univocal classification of pregnancy complications. The pathogenesis of pregnancy failures is linked to the thrombophilic effect of aPL but also to different mechanisms including a direct effect of antibodies on the throphoblast differentiation and invasion. The study of experimental animal models provided sound evidence of the pathogenic role of aPL both in lupus prone and naive mice. The definition of APS as a condition linked to high obstetric risk and the application of an effective therapy have completely changed the prognosis of pregnancy in these patients. In fact, despite the high number of complications and preterm delivery, today a successful outcome can be achieved in the large majority of the cases.