Pilot PARTUM Trial: Postpartum Aspirin to Reduce Thromboembolism Undue Morbidity

Inclusion Criteria: Study inclusion criteria includes one (or more) first order criterion or two (or more) second order criteria. A patient is still eligible if they have multiple criteria met, at the discretion of the local investigator. ONE (or more) First Order Criteria: 1. Known inherited thrombophilia diagnosed prior to enrolment: i) Heterozygous factor V Leiden, OR ii) Heterozygous prothrombin gene variant, OR iii) Protein C deficiency, OR iv) Protein S deficiency 2. Immobilization (90% of waking hours spent in bed) for ≥7 days anytime during the antepartum period TWO (or more) Second Order Criteria: 1. Postpartum infection 2. Postpartum hemorrhage (\>1000 mL of blood loss, regardless of delivery mode) 3. Pre-pregnancy BMI ≥30 kg/m2 4. Emergency or unplanned cesarean delivery 5. Smoking ≥5 cigarettes/day before pregnancy 6. Pre-eclampsia 7. Current pregnancy ending in stillbirth (pregnancy loss \>20 weeks gestation) 8. Small-for-gestational-age infant (\<3rd percentile adjusted for gestational age and sex). 9. Previous history of superficial vein thrombosis Exclusion Criteria: 1. More than 48 hours since delivery 2. Received more than 2 doses of low-molecular-weight heparin (LMWH) since delivery 3. Need for postpartum LMWH prophylaxis or systemic anticoagulation as judged by the local investigator. May include but is not limited to: 1. Documented history of provoked or unprovoked VTE 2. Mechanical heart valve(s) 3. Known antiphospholipid syndrome 4. Known high-risk inherited thrombophilia i) Antithrombin deficiency; ii) Homozygous factor V Leiden; iii) Homozygous prothrombin gene mutation; iv) Compound heterozygosity factor V Leiden and prothrombin gene mutation; v) More than one inherited thrombophilia 4. Need for postpartum aspirin as judged by the local investigator. May include but is not limited to: 1. Documented history of myocardial infarction 2. Documented history of ischemic stroke or transient ischemic attack (TIA) 5. Contraindication to aspirin including: 1. History of known aspirin allergy 2. Documented history of a gastrointestinal ulcer 3. Known platelet count \<50 x 109/L at any time during the current pregnancy or postpartum 4. Active bleeding at any site, excluding normal vaginal bleeding, at the time of randomization 5. Most recent known hemoglobin ≤70 g/L documented during the current pregnancy or postpartum 6. Known severe hypertension (SBP \>200mm/hg and/or DBP \>120mm/hg) during the current pregnancy or postpartum 6. \<18 years of age 7. Unable or refused consent