Antiphospholipid (aPL) antibodies (i.e., lupus anticoagulants and anticardiolipin [aCL] antibodies) are associated with obstetric complications. Recurrent spontaneous abortions and fetal death represent the obstetric criteria of the aPL syndrome. Intrauterine growth retardations, preeclampsia, and prematurity are other common clinical features not included in the syndrome. Overall, the prevalence of obstetric complications in aPL-positive women is about 15 to 20%. The presence of lupus anticoagulants carries a risk of recurrent miscarriages and fetal death ranging from and odds ratio of 3.0 to 4.8, whereas that of aCL antibodies ranges from 0.86 to 20. The mechanism(s) by which aPL antibodies causes these events still has to be defined. Thrombosis in the placental vessels, which causes placental hypoxia and eventually leads to abortion or fetal death, has been reported in aPL-positive women with obstetric complications. Impairment of embryonic implantation has also been proposed. Unfractionated or low-molecular-weight heparins, alone or in combination with low-dose aspirin, represent the current standard treatment of pregnant aPL-positive women to prevent recurrent obstetric complications. Upon treatment, the live birth rate increases from 0 to 40% to 70 to 80%. Despite these good results, heparin-treated pregnancies are still characterized by an excessive frequency of maternal and/or fetal complications, indicating the necessity of a better calibration of the dosage, duration, and timing of administration of heparin treatment.