(621) A randomized trial of unfractionated heparin dosing for thromboprophylaxis of prolonged antepartum hospitalizations

Thursday, February 9, 2023

4:00 PM – 5:30 PM

Objective: Pharmacologic prophylaxis (PPX) against venous thromboembolism (VTE) is recommended for extended antepartum admissions, but data on optimal dosing of unfractionated heparin (UFH) in pregnancy are limited. We evaluated the safety of standard versus gestational age (GA)-based dosing of UFH for VTE PPX in prolonged antepartum hospitalizations.

Study Design: This was a randomized trial of pregnant persons with antepartum admissions of ≥ 72 hours. Participants were randomly allocated to 2 dosing regimens: standard (5000 units subcutaneous (SC) every 12 hours (q12H)) or GA-based (1st trimester: 5000 units SC q12H, 2nd trimester: 7500 units SC q12H, 3rd trimester: 10000 units SC q12H). Serial lab testing (aPTT, anti-Xa, and platelet count) was performed. The primary outcome was the proportion of patients with an elevated aPTT ( > 36.2 seconds) 6 hours after UFH. Secondary outcomes included VTE events, and delivery and neonatal outcomes.

Results: From December 2020 to April 2022, 97 antepartum patients were screened, and 46 were randomized: 22 to standard (1 excluded after randomization) and 24 to GA-based. There was a significantly higher rate of elevated aPTTs in subjects on GA-based compared to standard dosing (33.3% vs 4.8%, p=0.02). GA-based dosing resulted in higher maximum aPTT (p=0.01) and anti-Xa levels (p=0.04). Receipt of GA-based UFH until delivery was also associated with higher rates of blood transfusions (36.8% vs 0%, p=0.01). There was no significant difference in VTE between groups (p=0.47). The median time to elevated aPTT was 14 days while on GA-based UFH, compared to no risk of elevated aPTT with standard UFH during the study period (p=0.05).

Conclusion: GA-based dosing of UFH for VTE PPX is associated with significantly increased rates of elevated coagulation parameters and subsequent bleeding risks. Our results suggest that if GA-based dosing of UFH is used for VTE prevention, monitoring of coagulation tests and heightened surveillance for bleeding risks are appropriate. Further study is needed into the role of individualized dosing protocols for VTE PPX of antepartum admissions.

Primary & Presenting Author(s)

Thalia Mok, MD
Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California, Los Angeles
Los Angeles, California, United States

Coauthor(s)

AN
Anissa Nguyen, MPH
Department of Urology, University of California
Los Angeles, California, United States
LK
Lorna Kwan, MPH
Department of Urology, University of California
Los Angeles, California, United States
CY
Colleen Yen, MD
Department of Anesthesiology, University of California Los Angeles
Los Angeles, California, United States
IS
Irving Steinberg, N/A
Department of Pharmacology, University of Southern California School of Pharmacy
Los Angeles, California, United States
NS
Neil Silverman, MD
Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Los Angeles
Los Angeles, California, United States
Rashmi Rao, MD (she/her/hers)
Assistant Clinical Professor
Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Los Angeles
Los Angeles, California, United States