Evaluation of a Risk-Stratified, Heparin-Based, Obstetric Thromboprophylaxis Protocol

Abstract

We read with interest the recent study by Lu et al 1 in the October 2021 issue. We believe the study provides important data on risk estimates for wound complications with heparin. Although this risk is well established, 2 this study provides an up-to-date estimate.We do, however, have a number of questions for the authors. First, the study was powered to detect a 65% risk reduction in postpartum venous thromboembolism (VTE), with a protocol that allocated heparin to 16% of patients. Did the authors anticipate that this 16% of patients would account for 65% of VTE events? And, if so, that heparin receipt would reduce risk 100% through 6 weeks postpartum? Additionally, the authors state that the VTE rate in the power calculations was similar to that observed but found risk to be 1.26 rather than the 2 VTE events per 1,000 deliveries anticipated. Given the lower-than-expected risk, would greater than 65% VTE reduction for the entire population be required with 80% power and two-sided a of 0.05? Finally, it is unclear to what degree inpatient postpartum heparin may reduce events weeks after discharge.