The aim of this study is to evaluate the efficacy of two dosing regimens of low molecular weight heparin (LMWH) to reach prophylactic anti-factor Xa levels in post-cesarean delivery women. Half of participants will receive a fixed dose of LMWH, while the other half will receive a weight-based dose. The hypothesis is that the use of a weight-based dose will result in more women reaching prophylactic levels.

Venous thromboembolism (VTE) is a major contributor to maternal morbidity and mortality. The immediate postpartum period is a high risk time for VTE, and cesarean delivery is an additional risk factor. In the United States, use of postpartum VTE prophylaxis with low-molecular weight heparin (LMWH) is commonly used but without a standard protocol or dose across all hospitals. A fixed-dose of LMWH is frequently used based on data from non-obstetric studies. However, there are concerns that in the postpartum population this fixed dose may not be adequate for prophylaxis.

This study aims to evaluate the efficacy of fixed dose versus weight-based LMWH to reach prophylactic anti-Xa levels in post-cesarean delivery women. This will be a randomized controlled trial (RCT) with half of participants receiving a fixed dose of LMWH and half of participants receiving a weight-based dose of LMWH. The hypothesis is that the use of a weight-based LMWH compared to a fixed dose will result in more women achieving prophylactic anti-Xa levels.

Inclusion Criteria:

• Cesarean delivery
• Meet facility guidelines for postpartum venous thromboembolism (VTE) prophylaxis: Presence of 1 major, or 2 or more moderate, risk factors.
• Major risk factors: history of venous thromboembolism, high risk thrombophilia, BMI ≥40, high risk medical comorbidities (heart disease, sickle cell disease, systemic lupus erythematosus, inflammatory bowel disease), cesarean hysterectomy, nephrotic range proteinuria, or cesarean intrapartum/during labor
• Moderate risk factors: BMI > 30, multifetal pregnancy, postpartum hemorrhage (>1L blood loss), tobacco use, non-laboring or elective cesarean, preeclampsia, infection, preterm delivery (< 37 weeks gestational age), age > 35 years, low risk thrombophilia, family history of venous thromboembolism, stillbirth, varicose veins, prolonged labor (> 24 hours)

Exclusion Criteria:

• Contraindication to anticoagulation
• Plan for therapeutic anticoagulation (antepartum or postpartum)
• Known renal dysfunction (Creatinine clearance < 30 mL/minute)