Venous thromboembolism (VTE) is a highly preventable but potentially fatal complication following gynecological surgery. The Caprini risk assessment model is widely used, but real-world evidence evaluating the net clinical benefit and cost-effectiveness of different prophylaxis strategies (mechanical vs. pharmacological) in gynecological patients with Caprini score $\ge$ 2 is still lacking. This study aims to evaluate the relative effectiveness of basic, mechanical, and pharmacological VTE prophylaxis strategies using a retrospective 1:3 matched nested case-control design. Furthermore, a decision tree model will be constructed to evaluate the incremental cost-effectiveness ratio (ICER) of these strategies to provide health economic evidence for optimizing VTE management pathways in gynecology

This is a two-phase study. Phase I is a retrospective nested case-control study. Patients undergoing gynecological surgery between Jan 2021 and Sep 2025 with a Caprini score $\ge$ 2 will be screened. Case group includes patients who developed objectively confirmed symptomatic VTE postoperatively. Control group will be matched at a 1:3 ratio based on age ($\pm$ 5 years), Body Mass Index (BMI), surgical approach, and benign/malignant nature of the disease. Conditional logistic regression will be used to calculate the adjusted Odds Ratios (ORs) for mechanical and pharmacological prophylaxis compared to basic prevention. In addition, uterus/myoma size and weight will be explored as potential gynecological-specific risk factors.

Phase II involves health economic modeling. A decision tree model will be built utilizing the ORs obtained from Phase I, combined with real-world cost data (prophylaxis costs, VTE treatment costs, bleeding management costs) and baseline incidence rates from literature. The Incremental Cost-Effectiveness Ratio (ICER) will be calculated to determine the most cost-effective VTE prevention strategy at different Caprini risk thresholds

Inclusion Criteria:

• Female patients aged $\ge$ 18 years. Underwent inpatient gynecological surgery (benign or malignant indications). Postoperative Caprini risk score $\ge$ 2. Complete medical and billing records available in the hospital information system.

Exclusion Criteria:

• Diagnosis of VTE prior to the current surgery. Currently receiving therapeutic anticoagulation for other medical conditions (e.g., atrial fibrillation, mechanical heart valves).

Inferior vena cava filter placement prior to surgery. Incomplete key clinical or financial data.

Female patients undergoing inpatient gynecological surgery at our center between Jan 1, 2021, and Dec 30, 2025