Abstract Background Anticoagulation is essential to prevent recurrent venous thromboembolism (VTE) during pregnancy in women with a history of preconception VTE. However, information on the safety of anticoagulant drugs in this setting is limited. Purpose To investigate the risk of maternal and foetal adverse outcomes associated with anticoagulant exposure during pregnancy. Methods Nationwide cohort of all pregnant women in Denmark with preconception VTE, 2000–2017. We linked individual-level data from nationwide registries on anticoagulant exposure, maternal and foetal outcomes. Results Among 5,099 pregnancies in 3,246 women with preconception VTE (mean age 31 years, 41% nulliparous), 36.4% were exposed to anticoagulants during first trimester (66.4% low-molecular-weight heparin (LMWH), 31.9% VKA, and 1.8% NOAC (Table). No maternal deaths occurred. Maternal outcomes were comparable among LMWH and unexposed women, whereas recurrent VTE and foetal loss was more prevalent in VKA and NOAC exposed women. Foetal risk was lowest in unexposed and LMWH exposed, whereas preterm birth was prevalent in VKA and NOAC exposed. Table 1. Maternal and foetal outcomes in pregnant women with preconception VTE according to first trimester anticoagulant exposure Maternal outcomes No anticoagulants LMWH VKA NOAC Total pregnancies/singleton foetuses, N 3,244/2,722 1231/1,124 591/442 33 /26 Recurrent VTE, % (N) 2.7 (89) 3.3 (41) 6.4 (38) – (<5) Antenatal bleeding, % (N) 2.3 (73) 2.7 (33) 1.5 (9) 0 Preeclampsia, % (N) 3.0 (98) 2.1 (26) 4.4 (26) – (<5) Foetal loss, % (N) 13.4 (436) 6.6 (81) 22.2 (131) 21.2 (7) Foetal outcomes in live singleton births, except stillbirth Stillbirth, % (N) 0.6 (17) 0.6 (7) – (<5) 0 Mean gestational age, days/birthweight, gram 246/3,458 246/3,471 238/3,212 243/3,138 Preterm birth (<37 weeks), % (N) 41.1 (1,111) 38.3 (428) 63.2 (277) 57.7 (15) Very preterm birth (<28 weeks), % (N) 0.9 (24) 1.3 (14) 2.7 (12) 0 Small for gestational age, % (N) 4.2 (109) 4.5 (49) 4.8 (20) – (<5) Mean 5-minute Apgar score, (sd) 9.8 (0.8) 9.8 (0.7) 9.8 (1.0) 9.7 (1.0) Congenital defects 8.4 (226) 9.0 (100) 10.0 (44) – (<5) Counts are supressed in cells with <5 observations to prevent disclosure of potentially identifiable information. Conclusion Our findings are reassuring and in support of the recommendation of LMWH for pregnant women with prior VTE. Few women were exposed to NOAC during pregnancy, and the safety of NOACs cannot be substantiated with the current level of evidence. Acknowledgement/Funding The Obel Family Foundation partly funded this research by an unrestricted grant.