Objective: Antibodies that recognize the phosphatidylserine/prothrombin complex (antiphosphatidylserine/prothrombin antibodies; aPS/PT) might reveal enhanced thrombotic risk in patients with systemic lupus erythematosus. Little is known about their association with pregnancy complications in the antiphospholipid syndrome (APS). Methods: We enrolled 55 patients with APS who were seeking pregnancy in 2 Italian hospitals. Antiphospholipid antibodies (aPL), including anticardiolipin antibodies, anti-β2-glycoprotein I antibodies, lupus-like anticoagulant, and aPS/PT antibodies were assessed, and the patients were prospectively followed for 24 months. Results: There were 65% (36/55) of the APS patients who had aPS/PT antibodies. Forty-seven pregnancies were followed, including 33 of aPS/PT+ patients. Forty-one of the 47 patients (87%) who initiated a pregnancy eventually gave birth to a child. The pregnancy duration and the mean newborn weight at delivery were significantly lower in aPS/PT+ than in aPS/PT- patients (33.1 ± 4.7 vs 36.2 ± 3.4 wks of gestation, respectively, and 2058 ± 964 g vs 2784 ± 746 g, respectively, p <0.05). Late pregnancy complications, including intrauterine fetal death, preterm delivery, preeclampsia, and intrauterine growth restriction (IUGR), were more frequent in aPS/PT+ patients, independent of the therapy. Titers of aPS/PT IgG were significantly inversely correlated with the neonatal weight at delivery. Vascular injury, as reflected by thrombosis, fibrinoid necrosis, ischemic and hemorrhagic areas, and presence of chorangiomas characterized the IUGR placentas in the presence of aPS/PT. Conclusion: The aPS/PT antibodies might represent markers of aPL-related pregnancy complications, IUGR/preeclampsia in particular, and could help identify beforehand patients who may require additional treatment. Copyright © 2018. All rights reserved.