Making Decisions about Thromboprophylaxis in Pregnancy: Women's Values and Preferences
Authors: Bates Shannon M , Alonso-Coello Pablo , Eckman Mark , Tikkinen Kari A , Ebrahim Shanil , Lopes Luciane Cruz , McDonald Sarah D , Neumann Ignacio , Zhang Yuqing , Jacobsen Anne Flem , Akl Elie A. , Santamaria Amparo , Guyatt Gordon H 
Published: October 2019

Abstract
Background: The risk of pregnancy-related venous thromboembolism (VTE) is increased in women with a history of thrombosis. Although antepartum low molecular weight heparin (LMWH) prophylaxis can reduce this risk; the baseline risk of recurrence and the absolute magnitude of the risk reduction with prophylaxis are uncertain. Further, LMWH prophylaxis is costly, burdensome, medicalizes pregnancy, and may increase the risk of bleeding. Therefore, uncertainty persists regarding the net benefit of thromboprophylaxis and recommendations about the use of antepartum LMWH should be sensitive to pregnant women’s values and preferences, which have not previously been studied.
Methods: We undertook an international multicenter cross-sectional interview study that included women with a history of VTE who were pregnant, planning pregnancy, or might consider pregnancy in the future. Women were classified as high (5 to 10%) or low (1 to 5%) risk of recurrent antepartum VTE. We ascertained willingness to receive LMWH during pregnancy through direct choice exercises involving real-life scenarios using the participant’s estimated VTE (high or low) and bleeding risks, hypothetical scenarios (low, medium and high risk of recurrence) and a probability trade-off exercise. Study outcomes included the minimum absolute reduction in VTE risk at which women changed from declining to accepting LMWH, along with possible determinants of this threshold, and participant choice of management strategy in her real-life and the three hypothetical scenarios.
Results: 123 women from seven centers in six countries participated. Using a fixed 16% VTE risk without prophylaxis, the mean threshold reduction in risk at which women were willing to use LMWH was 4.3% (95% CI, 3.5 – 5.1%). Pregnant women and those planning a pregnancy (compared to those who might consider pregnancy in the future) and those with less than 2 weeks of experience with using LMWH during pregnancy (compared to those with more experience) required a greater risk reduction to use prophylaxis. In the real life scenario, there was there a significant difference in the proportion of women choosing prophylaxis between those at high risk (87.1%) and low risk (60.0%) of recurrence (p=0.01). The proportion of women choosing to use LMWH prophylaxis was 65.1% for the low risk hypothetical scenario (4% risk of recurrence), 79.7% for the medium risk scenario (10% risk of recurrence) and 87.8% for the high risk scenario (16% risk of recurrence).
Conclusions: Most women with prior VTE will choose prophylaxis during a subsequent pregnancy, regardless of whether they are categorized as high or low risk of recurrence. Nevertheless, 40% of lower risk women will decline LMWH, as will over 10% of high risk women. Thus, these results mandate individualized clinical decision-making for women considering LMWH use during pregnancy, and weak guideline recommendations for LMWH use that highlight the need for individualized decision-making.

Disclosures
No relevant conflicts of interest to declare.