Objective: To compare severe pregnancy complications in ART singleton pregnancies treated with anticoagulation due to thrombophilia to low-risk, spontaneously conceived untreated pregnancies. Design: Retrospective case control.Setting: New York Presbyterian-Brooklyn Methodist Hospital, Brooklyn New York.Patients: 615 ART pregnancies compared with 391 low-risk, untreated pregnancies matched for age and time of delivery.Interventions: ART pregnancies were treated with LMWH and low dose aspirin daily and managed by MFM specialist during the entire pregnancy. Main Outcome Measures:Compared for intrauterine growth restriction (IUGR), preterm premature rupture of membranes (pPROM), thrombocytopenia, prematurity, preeclampsia, abruption, and fetal death. Results:The incidence of IUGR was significantly lower in the ART group (5.05% vs. 9.21%, p<0.01). Preeclampsia was significantly reduced in the ART group in comparison to the control, 1.14 % vs. 6.39 %, p<0.0001. PPROM was significantly reduced in the ART group in comparison to the control, 1.46 % vs. 7.67 %, p< 0.0001. Prematurity was reduced in the ART group, 3.43% vs. 9.72%, p<0.0001. Thrombocytopenia incidence was similar, 2.28 % vs. 2.05 %, p > 0.8. Abruption was similar in the two groups, ART 1.3 % vs. 1.02 %, p >0.68. There were more fetal deaths in the control group but due to the small numbers in both groups, statistical comparison was not possible. Conclusion:Use of antithrombotics in ART conceived singleton gestations complicated by thrombophilia under MFM specialty care resulted in significantly decreased prevalence of most major obstetrical complications when compared to low-risk unselected untreated pregnancies.